I think new aftermarket/performance exhausts for mk1's are mostly unavailable or no londer produced these days. I think you can still get new ones from Oreca or OMP though.

If it's making 167 I'd presume it's got Piper 270 or similar profile cams in it, removing the distributor will let you look at the end of the exhaust cam, it will have numbers stamped on it to indicate what cams they are