The exhaust ports are a major restriction on B20 heads, so I'd ask Isky to grind you one that combines the W-71 on the inlet & the larger W-81 on the exhaust. Next step after that would be to choose an intake lobe with more lift than the W-71 rather than more duration, but you'd need larger valve springs than the duals that Isky sell for Volvo. (I've always used the Isky 'Grey & White' springs for SBC's on mine, not the ones that Isky sells)

2" exhaust is too small for 4-1 headers to function properly too, I'd use 2.25" up to the muffler, then 2.5" mufflers.