Pretty much anything is better than the single downpipe manifold the PV would have come with.

From what I understand the 4/2/1 header styles work better at the RPM's most of us would normally use on the street, the 4/1 style works better at really high rpms.

The dual downpipe manifolds are quite nice, basically a cast 4/2 portion of a header, with the downpipe being the 2/1 portion. Only issue being the diameter on the single pipe section if you have a lot of HP.

For whatever reason, Volvo somewhat choked the heads in the exhaust ports. Probably intentional, to keep the HP levels down in a hard to change spot. But that means that you can't really 'uncork' a lot of power just by swapping the exhaust. Until you've sunk some effort into improving the flow in the head, that is.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)