I have a cross-over pipe on my '68 Chevy 292, w/ Clifford headers. Not really an "H", more of a Russian "N", as the collector from 1-2-3 is spaced ahead of the collector of 4-5-6, and the angled pipe is spaced accordingly.
I was told by the mechanic that this trick would increase torque in climbing situations. Never dyno-ed, but seat-of-pants says it works.

I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.