How come it's going to be too much for a 1600 i don't get it, some of the we stores I've seen the exhausts suggest 1300-1600 motors is this for legal purposes? I dunno anyway I'm new to air cooled VWs so this is all the learning curve
If your engine is stock, meaning 1584cc, stock VW cam, stock carburetor etc... here's some information.
Your exhaust valves valve opens 44.5 BBDC. The stock engine made peak HP @ 4400rpm.
the "ideal" exhaust for the above would have primary pipes of 1.27" ID, and primary length of 40.37". The pipe after the 4-into-1 collector would need to be 1.71" ID (pipe from flange to muffler).
By tuning the engine with common bolt on's to move peak rpm up to 5000 (high lift/ratio rockers, Weber 40IDF's, 4-into-1 header and free flow muffler, centrifugal adv distributor) you can move the pipe ID to 1.35" and muffler pipe size to 1.82"
I'm not saying to hunt a header made with these exact sizes (good luck), but from a scientific perspective, this is why a stock motor isn't best muffled by one of the big turbo or straight thru mufflers.
Hope this helps,
Jim