Any guidance on my 1970 Duster plans

I like the idea of using the T/A motor, provided you don't grenade it. Unless you need a cash source to finance the build, then I would sell it. Otherwise, drop it in and have a cool piece of history between the fenders.

I like the idea of a T/A or AAR style Duster, just don't put badges on it that say that. But reinforcing the TB suspension makes complete sense for that style build.

As Blu said (beat me to it), if you plan to autocross it, start planning for 17" or 18" wheels as the available tires for the smaller wheels are not performance oriented. I like big brakes and 18" wheels allow for 14" or maybe 15" rotors and you can fit a 275/35R18 on the front without any real body work or flairs. BTW, the big dogs at the Optima event at SEMA all seemed to be running 315/30R18's.

I would suggest PS for autocross, but it's just my gut feel not based on experience. I would guess a manual box would wear you out before a single lap, and I doubt even the 20:1 manual box would be able to keep up with the corners. I would go right to the Borgeson box myself.