BBC in 72 4X4 motor mount ?s

[GM72K10]

Ok
To make a long story short, last year I got free, yes free a 72 GMC K2500 4x4 454 auto TH400, 3:73 gears, but MINUS the engine. As if I needed another one but free is real hard to say no at. The engine was in it when I first looked at, so I know this set up did work. The truck was inspected and running. The cab has gone to old Rusty C10 (needed a lot of work), bought a 72 C20 with a 402 Th400, low mileage, fixed that cab, have put the 402 in the frame with new motor mounts, am ready to put cab back on. QUESTION! Exhaust manifold hits frame, just barely, on driver's side. Don't have the motor mount pads from the previous engine, just bought new ones from NAPA, what needs to be done to make manifolds clear frame? By the way, this truck has original NP205, and every thing is moved forward so there is more clearance between firewall and back of engine already.
Thanks in advance
GM