If its a factory motor its a 273, the 440 will fit read very tight a hemi will fit in there. The motor is very heavy for that small car and will be a pain to work on but it will scream in a strait line, keep it out of corners.
They put 383 in 67-69
440 in 69 and hemi's in 68.
A lot of people are putting the 380hp crate motor in these as the only motor avalible in a 67 b cuda were the /6's and the 2 and 4bbl 273
Sounds like a cool car lets see pictures