Oh I am sure it holds up. Look at that job autoxcuda did on his intake. That looks great. I don't know why he simply didn't use the thin metal plate to convert it, but what he did looks really good.
A square bolt carb will bolt directly to that spread bore M1 intake.
But the idea is for the air to have a straight flow path down the intake. Buy leaving a divet or crevice for the wider spread bore, you could get turbulance and fuel puddling. Honestly it's probably overkill. I doubt even measurable on a dyno.
But ns1rm21 did it on his 440 M1 intake and he noticed the idle quality get better. No other changes. Also before he filled the gaps he would see gas stains and wetness in those spread bore gaps, especially when running race gas.... So we did it with my SB M1. Only cost was the Moroso AB expoxy and we had a bunch leftover because a pushrod pinch hole repair. So what the heck.
For having a single plane intake, a warm cam, double pumper silver claw carb it's really no brainer putt around town street friendly. It will first crank start from dead cold in the morning after sitting a week. And if I'm really in a rush, I don't even wait to let it warm up before I leave. No choke either. Now that is not all just because of this intake mod. Not hardly. But it's a lot of little things adding up.
