Just had some Eddie Rpm Perf heads cleaned up by a local speed shop for a 69 440 bored 50 over w/ solid cam .540/.558, 10.25:1 compr. When I asked if gasket mattching the ports would help me get more out of the motor, they told me a gasket match on the intake side only but not the exhaust side. Anyone know why?

 

The reason is probably two fold:

First in many cases -particularly when headers are fitted- ports which are not gasket matched are usually smaller than the pipe they will feed into. This won't hurt flow especially seriously unless you're NasCar racing or similar.
This leaves a step down into the header/exhaust system which gives the nice little benefit of stopping the exhaust pulse which is reflected from the exit end of the exhaust back up the pipe to the head. If this pulse is timed correctly (by tuning the exhaust accordingly) it will help drag the next cycle of spent gases out of the cylinder making the cycle more efficient.
If the pulse comes at the wrong time, it will collide with the outgoing gases and hurt flow significantly. If you can't tune the exhaust (to a specific HP/RPM) then it's better to have the reflected pulse stop before it reaches the cylinder.

Secondly and not as complicated -often gasket matching the exhaust side will require lowering of the exhaust port floor which very often will also hurt flow, even if done very nicely. You gotta know exactly what you're doing as you'll undo all that nice work done by the speed shop.