Timing and Carb after exhaust
 

My 76 Trans Am 455 starts and runs great. One flick of the throttle to set the choke and it starts right up without stepping on the pedal. Idles like a rock at 750. A few years ago, I took my time and tuned with a vacuum gage getting the carb and timing in sync as well as I can. Engine is completely stock internally, with a stock Q-Jet, recently rebuilt to stock specs. I don't think it's ever been apart.

The current exhaust is the stock logs, with a small aftermarket dual exhaust (no H or X) and a single cross-flow, dual in-out. This was put on by a previous owner, so I don't know the details. Looks to be a crunch bent 2" exhaust at best, I can get my fingers around the pipes at the bends, no problem.

I have a set of HO manifolds and the 2-1/2" 89021 Thrush dual with H-Pipe system ready to go on in the fall.

Will the engine need timing/carb adjustments after the new exhaust is installed?

If so, what direction do you typically have to go (advanced/retarded, more or less fuel at idle)?