How rare are the Yokomo magnesium parts today?

[V12]

I got an used Yokomo YR-4 touring car in well used condition and thought of restoring in the first place.

Now I realized this is an early version with magnesium front and rear gearboxes and magnesium motor mount.
I have not seen such magnesium parts in a long time but remembered my Yokomo YZ-870C also came with those parts.

What do you think how rare are such parts today?
Also what would make more sense, restoring the YR-4 car or using as a donor car? For suppling the magnesium parts to a YZ-870C?

[Toaster]

Now I am no expert, just a Yok fan but the mag parts are a little rarer these days. With the 870 reissue which has definitely lowered the cost of parts for that model, I would perhaps hold onto them for a later rebuild (in my opinion of course) like a 91, 92 etc

I have gutted a number of yr-4’s for this very reason and sometimes feel a little bad given all the parts for them I have laying around but it has allowed me to finish off a number of period correct and upgraded yz10’s.