I know some stuff about these, but maybe not all. I owned one. It was glorious. Picture of mine:
I'm scheming about the next stage rally car and these are on the short list. Here's an overview of what the plan would be, as of right now:
Suspension:
-Front 8.5" travel custom struts built around a Bilstein 40mm inverted damper (I have these on the shelf currently as spares, and have made similar struts for the Merkur) [stock travel is 7.25"] and boxed stock control arms
-Rear 10" travel coilovers (Afco, Bilstein, or Fox), turrets tied into cage, equal length 4 link made with circle track parts, reinforced stock axle initially with eventual plan to adapt Toyota pickup axle
Chassis:
-Buy a car from somewhere without road salt
-Typical FIA 253 rally cage, tied into strut towers. Reinforce everything that sees suspension loads. Seam weld.
Drivetrain:
-Stock 22R and 5 speed initially (tough as long as you don't rev it high enough to fling rods everywhere, just slow)
-Eventual plan for Beams 3sge and J160 6 speed (to go in with truck axle)
Brakes:
-Stock discs up front, convert to discs and Supra calipers in rear. Reassess if this seems like it's not enough, but this would allow for 14" wheels and therefore lighter tires.
Known issues:
-Weak steering arms. Solve with big billet CNC ones (they are a bolt on part).
-Chassis weakness. Tying the cage in everywhere would be important. Double plating all attachment points, etc.
-Parts availability. Many parts are shared with the Supra and AE86 meaning there are aftermarket options, but there are probably holes in availability.
-???
Tell me why not. The car would be built in two stages, with chassis/suspension prep happening from the start and then an engine swap and truck axle when I have the parts. Entire shell would be 3D scanned at the start of the project to allow parts to be designed later.
Yes, I drank too much coffee this morning but I'm excited about this. Picture for inspiration.