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Here's something I started a while ago and which takes inspiration from some projects show-cased on this site.
The chassis is a traxxas item... TRX-1 I believe. I drilled some new holes to make it accept the Kyosho pro-x front bulkhead, a Yokomo YR-4II rear gearcase and Academy Wyvern center transmison case and motormount.
The kyosho and yokomo parts were picked to give the startpoint for the quadra-symmetry: equally spaced inner hinge pins for the suspesion arms. Talking of which: the front arms are traxxas items again; I think blue eagle LS or LSII? The rear arms belong with the yokomo 870-C. They are the some length from inner hinge to outer hinge: step 2 for the quadra-symmetry.

Combining the academy motor-mount and central transmission to the yokome rear transmission case allowed me to bring the motor more over the center of the car; both sideways and front-aft.
For the topshaft I used a different duratrax item to bring the spur closer to the center and adding dual slipperpads in favour of the academy single-pad slipper. Hopefully the spur can fit under my body of choice; I have no gearcover for it. The diff is from the academy wyvern and requires no cut out from the chassis, plus it puts the output centers nicely over the hingepins. And best of all: I have both a gear and ball version of this one. The belt is afrom the wyvern again: plenty spare and the perfect size coupled with a ball bearing as belttensioner.
The rear axle carriers are Tamiya M-chassis items and take the wheel further outward to compensate for the different wheeloffset between the old 870-C rims and modern rims I prefer. In the front I have ultima carriers and steeringknuckles for now.

Time for an update: I finished the suspension and started on the steering setup.
Still not happy with the steering setup: too much bumpsteer
I'm divided regarding the electronics lay-out too: a lot will depend on which body I'm forced to use to clear the spur and motor.

Picture time:

I like that

Try attaching the inner links of your tie-rods to ball-studs on the bottoms of the bellcrank instead of the tops, that might eliminate or at least significantly reduce the bump-steer. It looks like your tie-rods would be more close to parallel with your front arms that way.

Glad you like it Lars; it took a lot of time and many trials before things finally started coming together.
Last night again I spent most of the evening test-fitting 3 different bodies: even opened up an original Kyosho bag with a Triumph replacement body. But in the end I came back to my original choice and cut the area that interfered with the spur.
I hope you like it even better now? Thanks for the advise Marc. I actually already solved the problem to the best I can do when you replied. Here's some extra pics of the steering just for you.
As you can see there's really not enough space between the belcranks and the chassis to mount the links underneath.
Maybe if I had raised the belcranks first, but I believe the links would hit the chassis when turning if I lower them on the inside. So instead I replaced the steeringknuckles with traxxas ones which raise the steeringlinks at the wheel side.
On top of that I added a locknut between the knuckle and link to raise the link further. It still isn't 100% perfect, but I can't raise the link further without weakening the steering or interfering with other parts at full turn.

Pretty cool. I wanted to do a dirt oval build that was very similar...using a YZ10 rear but with a Triumph front for the adjustable kick-up.

The only thing that might hinder your design is that the motor is pretty far forward off the rear wheels, and that might hurt your rear traction.

That would be the other way to achieve a more parallel tie-rod...good job. There's another possibility you could swap the upper and lower parts on the servo-arm end of the crank, which would raise up the tie-rod inner links while keeping everything else the same height. You might have enough room to mount the tie-rods underneath the inside links if you used open-ended ball-ends instead of ball-cups and low-profile ball-studs, or even go a step further towards low-profile by cutting off some of the base of a 4.8mm ball-nut and using 3mm hex-head screws and threadlock to screw the threaded ball part of the cut-down ball-nuts onto the protruding threads of the 3mm screw. (I hope that makes sense the way I described it...PM me if my description sucked.)
I used that trick for both the servo arm and the center links on the Optima, clearance is very tight in those spots.

Phin wrote:Pretty cool. I wanted to do a dirt oval build that was very similar...using a YZ10 rear but with a Triumph front for the adjustable kick-up.

The only thing that might hinder your design is that the motor is pretty far forward off the rear wheels, and that might hurt your rear traction.

Hey Phin,
The YZ10 drivetrain is really great, both in 4WD and RWD. But, while I understand how cool it would be to have an adjustable kik-up, the triumph front is fragile and maybe not as good a design for oval racing.
Talking about oval: while I used the academy parts to bring the moter closer to the center, you would probably prefer to do the opposite: put the moter further to the left. and it's perfectly possible if you shift the yokomo motermount outward and swap the rear diff over. (Ofcourse You would loose the capacity to run 4WD, but that's where you seem to be going for anyway)

Yes, on mine the moter is further forward than on the stock 870C transmission.
I mostly run on astroturf and the tendency there is to have the moter further forward. Cars such as the YZ2 etc are all the big thing.
So I'm just imitating the masses in my own little crazy way

Here is is an earlier project in which I used the yokomo rear drive train and a 2WD front suspension:


link for more detail