Just got my New Dart SHP 4.125 Block for my 33. I am building a SBC 400, AER 210 Heads, thumper Hydraulic roller cam and EZ EFI. This is a mild build at 500HP, nothing like my fire breathing 532HP solid roller 383 I have in my 69 Camaro. I found some headers for SBC that have 1-3/4 primaries. Summit has Sanderson Headers CC1-134-P - Sanderson Headers Blockhugger Headers for hot rods. This would be a help for large HP SBC.

Well good luck on your build

TomH33