OldIHC

I just noticed that the exhaust pipe from the motor to the muffler is about 3" dia and from the muffler to the tail pie it is about 1 3/4": would this cause an issue?

When the exhaust exits the manifold, it's extremely hot. The front exhaust pipe radiates a lot of that heat, and more is lost in the muffler.

Considering the diameter of tailpipes and intermediate pipes on comparably sized sixes from the same era, the 1-3/4" is probably sufficient. The 3" front pipe will decrease the velocity of the exhaust, and cause it to shed some heat. The smaller tailpipe will likely increase exhaust velocity a tad, but not cause backpressure problems.

These engines turn about 3600-3800 rpm maximum...not exactly a race engine by any means.

Thanks for the information much appreciated.