Its not a 400M per say. But the family is the 351M/400 so just about every one called it a 400m. I've had Ford parts guys ask if it a 400M over the counter.But your right its a 400
Back in 79 (yea I'm that old) my boss bought a 2WD F250 with the 400m, He wasn't to happy with the way it ran. So we warmed it up abit. Hot RV cam and kit, roller chain kit, Alum. 4 barrel intake manifold, good street headers, reworked the dist. for the advance we wanted ( note, the vacuum...
The 2 to 4 adapters don't work period. They were for putting a 2 barrel on a 4 barrel manifold. Them someone got the idea to turn them upside down and put a 4 barrel on a 2 barrel manifold. Which worked after a fashion. You can't make 300 to 750 CFM go down a hole made for 300 CFM maximun. Plus...
I just found this site. My good luck. Been a ford fan since 55, 1st ford a 49 coupe, Latest in house resterations are a 78 2wd 460 F250 and a 79 F250 4wd w/a brand new 390.I own my own shop here in Wrangell Ak. Current driver is a 94 F250 4wd King cab.