Look at the floor hump a A/T car don't have a hump you can buy floor humps for chevelles I don't know abut montes but if it jest has a hole hacked into the floor its not a real 4 speed car
It sounds like the intake gasket is shot I would do a cylinder leak down test or some compression testing to make sure the head gaskets are bad why do them if you don't have to
Well I got mmy 70 monte on the lift after I got it and it has a 8.2 10 bolt non posi with 3:73 gears form what I know iv never seen nothing but 12 bolts. Under the montes iv looked at what do you guys think