I did some searching and can't seem to find a spreadbore manifold for Magnum heads. I'm currently running a dual plane M1 with an Edelbrock 1400, but I'm partial to Thermoquads. I can run an adapter plate, but I haven't heard many good things about them in terms of performance and mpg. Correct me if I'm wrong. I'm not going to pull the heads to redrill them for an LA manifold. Anybody know of anything?

I run a Thermoquad on my M-1 using an adapter plate. Works well and I get great gas mileage. Is it the best for all out performance? No.

My understanding was that an adapter was fine as long as it was an open type and had been properly blended to the intake...

Wow, thats very interesting. I always thought they were pretty much junk. I have an open style Mr Gasket spreadbore/squarebore adapter plate laying around. Maybe ill cross my fingers and use it to revive my Thermoquad. That thing ran like fuel injection once I set it up