727 poly engine transmission

I'm resurrecting this old thread cause I'm curious about something. There is a '66 with a 318 poly and auto that I'm kind of interested in. I'm not a fan of the poly motor, and if I went for it I would probably replace it at some point with an econo-build small-block like in this Moparts forum http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=3944014&page=0&fpart=1&vc=1

I don't know what model auto trans came behind poly 318's in '66 - 727 maybe? Is the bellhousing bolt pattern and overall dimensions of the trans behind the '66 poly 318 the same as the one behind a '66 273? So if I am reading the previous posts in this thread correctly, it sounds like a econo-build LA or Magnum small-block would bolt right up to the '66 poly 318 trans that is already in the car - does that sound right?

In the interest of squeezing the max economy out of the car I would eventually replace the existing trans with a 904 or a newer one with a lock-up converter and overdrive. The upgrades would have to be done in stages though as my budget allows so that's the reason I'm curious if a newer engine would bolt up to the poly 318's existing transmission. Thanks for your help.
http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=3944014&page=0&fpart=1&vc=1