I think I'm learning here, but correct me if I'm wrong. I can take my tranny out of my 73 comet and put it in a 75 maverick right. Without even using a BFH.
There are slight differences between the bell housings for certian motors though. There is a small bell housing (170,200 6's) and a big bell housing that fits the 250 6 and the v-8 302.
They will fit in all mavericks its just that some bolt to different motors. But the bellhousings can be interchanged.
the trans will be the same, but the bellhousing may be different depending on the size of the 6 cylinder
250 (I6), 302, 351 C or W... All interchange. If the I6 is a 170 or 200, then tranny will swap, but only with the bigger bellhousing.