I've been doing some reading and all, it seems, of the long-tube type have ground clearance issues once you go up to a 1 3/4" primary.
A 1 5/8" primary SAP for a SBC gen I doesn't cover, fully the D-port on the LT1 head hence needing to go to the slightly larger 1 3/4" - which is what limits the choices massively.
As far as I know, Hedman are the ONLY company to do 1 5/8" D-port matching headers for the Third gen - ie. LT1 in Third Gen set-up.
Hedman do both Long-tube and shorty headers.
The long-tubes have ground clearance issues and do not have a Y-pipe to fit them.
The short-tubes (eg. 66479) obviously provide maximum clearance AND there's a Y-pipe kit (17470) which is an almost bolt-on (you need to weld/clamp on one end).
The stainless works long tubes do NOT work with the T5 and, apparently, only clear the T56 with collector modifications.
However, looking at the pictures on Hawks and Spohn it looks like the Headers will clear the T56 but the Y-pipe for that kit definately WON'T.
To make matters worse the Spohn T56 adapter X-member is pretty huge and I'd guess kills the clearance further.
So if I used the Stainless works headers I'd need to have a custom (stainless) system made up - which is a ball-ache - but would be extremely difficult as the S/W headers tuck so far up into the trans. tunnel.
I'm now considering the Hedman shorties so I don't have to concern myself with ground clearances OR potential gearbox clashes . . . . .
That said I really wanted long-tube headers.