I have a set of their assembled heads and stainless rockers going onto a stock bottom end budget 360 build for my wagon. Hoping to have it running by late May, just waiting on some parts right now to finish the motor.
I had their air gap copy manifold and returned it after reading it leaves close 30hp on the table compared to a real air gap...Ended up with a single plane instead for my build, but some parts don't justify the savings benefit in my opinion. I was going from 318 iron heads with 1.77" intake valves that I sold for $300 local, so the $900 for the assembled Speedmaster heads were a no brainer, and so far on disassembly they have checked out okay.
I had that air gap intake on a stock stroke 318 enginemasters build that I bought that pumped out 477 horsepower. Under 10.5 compression, pump gas, flat tappet cam, etc, etc.
Ran mid 11’s in a 3400 pound car with a smaller camshaft than was used in the competition.
Those intakes may well make less power, but they make more than enough for 95% of the guys who are going to run a dual plane to begin with. That little motor I had more than proved it.
Makes me wonder why the two extremely sharp guys who built this motor and took it to the competition left 30 horsepower on the table. Hmmm
https://www.motortrend.com/how-to/0901phr-mopar-318-magnum-engine/ 
