Tri-y big block headers

I’m open to all recommendations.

You might try contacting the outfit that modifies(d) Tri-Ys for 4 speed use. Maybe they can provide some info..….
Welcome to Accurate Exhaust Products, Ltd

Depending on how things work out for me, I may have my unmodified set available, but not till late spring.
FWIW, A while back, a post here shows how one member modified his driver side for torque shaft clearance needed unless you run a hydraulic release bearing. You'd need to search for it to know what it took.