Big block exhaust

Long time viewer/first time poster and need a little advice. A year ago I picked up a 68 dart GT, it was just a rolling chassis, no motor or transmission but has a 8-3/4”. It was originally a floor shifted auto. Now I am picking up all parts needed, recently I grabbed rebuilt big block 400 and a 833 4-speed and need to piece together the linkages and such. I am debating on which headers to go with and think I narrowed it down between the Schumacher & TTI’s because I would like to run power steering and possibly power brakes and I don’t want to mess with fender well headers for a variety of reasons. My ultimate goal is to eventually be running 500-550 HP thru stroking the 400 and the car will be mainly street.

My question is two parts. Are the smaller tubes on the Schumacher that big of a deal as compared to the larger TTI’s given my goals?

Also TTI sales a z-bar to deal with the 4-speed fitment issues, anybody know if that z-bar would work with the Schumacher as opposed to modifying the header or stock z-bar? (since I don’t have the z-bar yet figured I could get the modified one to begin with)

I know there have been similar posts as far as what headers to use, but my biggest curiosity is the fitment issues associated with a 4-speed

Thanks!