You have a lot of questions there and some variables with our answers.
The intake will work on a 273 as long as the heads are 66 and newer. 64 and 65 heads had smaller bolts and they were at a odd angle. the early heads has 1/4" bolts where the 66 and newer were 5/16". The mis match between larger ports and the smaller 273/318 ports isn't a real issue.
