Dart 318 Header opinion

Longer tubes provide greater benefit lower in the rpm range and shorter tubes higher in the rpm range. However even the shorty and block hugger tubes are at least as long as any of the cast iron small block manifolds - so in that respect the headers will not hurt performance.

I've run Pipemax for both stock 340 and with my current cam which is only slightly bit more radical than yours. So I can tell you that even for a bigger motor the 1.625" primaries are plenty big, and 2.5" Collector is OK. Ideally, you probably would be best off with 1.5" primaries, but ideally you'ld also be building equal length tuned headers out of stainless... In other words, I think for your purposes, you'll be fine.

TTI also has a shorty header in roughly same price range* and unlike the headman you won't have to modify it.
*depending on coating and shipping - the latter which I have no idea about how much that might add to your place.