Need help with bbc manifolds and clutch linkage

[chevytrucking]

I've got 69 chevy 1-ton roll back car hauler that's had a 383 and 4spd in it for a long time, but it's just not enough motor. I pulled it out, dropped in a 454 out of a 85 GMC truck. I've got everything converted over, just about ready to fire it up, but I can't figure out what to use for exhaust manifolds.

I've got the z bar type mechanical linkage that sits right below the back exhaust port. I've got two different sets of manifolds and they won't fit. I bought a set of Summit block hugger headers, they don't fit.

This isn't a high rpm application, it's strictly low rpm towing torque I'm after, so cast iron manifolds are just fine. What did these trucks use when they were new? Nobody I've asked seems to know. Google image searches don't produce anything.

Help!