Wisefab isn't completely out the question.. I'm going to make a Supra subframe fit my Altezza so I can use wisefab
And as above, Figs Engineering do a lock kit too.
Rear arms & bars etc are also available from Figs, and Megan Racing and few other places..
You can also cut and weld your steering knuckles for a cheaper way to obtain more lock, aswell as lock spacers.
Regarding engines, yes the 300 is a 2jzge, vvti, and awsome.. It's easy enough to turbo it should you want to.. Although the standard management can't deal with boost so you'll need an aftermarket ecu that can.
Iv done a fair few 1jzgte conversions which work very well, not a cheap exercise though.
Bodywork parts are easy to get, I have a full Touring Car Bodykit for mine, my friend makes & sells the kits.