can I mount
 

I have a 1979 12a n/a drive-train. Is it possible to marry a 1984 12a motor that originally came with an automatic transmission to it? My 79 motor needs rebuilding and found a 84ish for sale for inexpensive. Will my flywheel fit onto the younger motor? I'm having a difficult time finding any info in the area, I guess it's not a common question. Thanks for the help.

yes and no....
the counter weight is built into the flywheel on the manuel engines so you will need an 84-85 flywheel and clutch setup.

or

an aftermarket flywheel. You remove the auto flex-plate and install the flywheel. (the auto counterweight is a seperate peice so you bolt it on to the new flywheel)