Thanks, Doug. I have a brand new set of 48DCOEs in the shop, and a partially completed side-draft intake manifold. Then life got in the way and I never finished it for the Pantera. But I ran a pair of adapted 40IDA 3-C Webers on my street Corvair for a decade, and they needed a choke not just for starting but until the thing was thoroughly warmed up. Or I got occasional bucking and popping. That was also the case with 40TIN Zenith 3-bbl weber-lookalikes.
My experience, as well as several San Jose Porsche owners with downdraft Webers: if you run paper or especially foam air cleaners and get a stack fire, the long aux venturis are cast pot metal and will instantly MELT. The molten metal then gets sucked down the intake and past any open intake valves into the combustion chamber. Then it solidifies.
On the next stroke, the pot-metal lump get pinched between the bottom of the piston & the squish area in the head, and cracks the piston, also breaking the top ring & maybe scoring that cylinder. So I had to overhaul the engine because of a backfire. IMHO, K & N oiled fiber air filters are not as good as paper at cleaning the air, but they don't soak up reversion gas either. That's what the Nor Cal air cooled Porsche guys use.
Like you, I found in the '70s there was no such thing as a specialty carb place. Most were racing teams or an occasional dyno shop. Good carbs, adjustable-everything but parts were/are expensive. Five jets, two air bleeds, a replaceable main venturi and replaceable emulsion tube- FOR EACH CYLINDER! Easy to get lost in the possibilities. Today I would be good friends with Jim Inglese and a local dyno shop instead of DIY.