good thread by the way. I'm jealous of your cad ability
Me? The stuff I did is simple, the good looking components of my model come from other folks that have made contributions. Just making tubes and arranging them can be a bit frustrating but not really hard. Grab that stuff and make it into what you want. If you can even contribute one little part to the SketchUp library we have then it's progress for everyone. Plus it will be there forever...
In one sense I'm at the same place you are with some choices right now. Choosing rear end parts. I have drawings for Ford IRS stuff and also Subaru. It's looking like the Ford Thunderbird style IRS uprights won't fit inside a 13" rim. That's too bad because 13" racing slicks are pretty cheap and probably the best match for these cars in terms of expected weight and rubber softness etc.
To break things you need to look at engine torque at one end and then tire torque at the other end. One can't really be bigger then the other, outside of inertia. The other issue would be spinning one rear wheel severely and over working the insides of your diff. Let's assume hard use, but not abuse.
I'm aiming for under 1700 lbs. with a small V8 and a driver and more then %50 rear weight bias. That would come to 500 lbs. per rear tire. You can use numbers from 1.0 to 1.5 for coefficient of friction for tires, from street tires to racing slicks. I am a little unsure of the those numbers, but it's a neighborhood. If you had 24" diameter tires, 12" radius, you could get between 500 ft.-lbs. to 750 ft.-lbs. of torque from either wheel.
So you need halfshafts and wheel studs etc. that can take that much. A street Subaru weighs more though so it would be able to generate something near twice as much stress on those parts. Working thru the problem the other way you multiply the engine torque thru the 1st gear reduction and then the differential reduction. In round numbers that would multiply the engine torque by about 10. So you know the street Subaru can generate that amount of torque on the halfshafts etc. in first gear.
I'd like to know if the stronger Subaru turbo models use heavier duty rear end parts, do any use the R-180 diff or bigger halfshafts? What years and models so I can try to find out more about the parts?