so whats the general rule with the small pattern vs large pattern flex plates? i have seen small ones on big blocks and large on small blocks so is it just whatever ma mopar had or is there a general rule?

It depends on the torque convertor size. 12" TC had the bigger plate and the 11" had the smaller plate.

904's will always have the small bolt circle, 727's can have either large or small up to '78 at which time the large circle was discontinued.

318 can be large or small.

340 will be small.

360 can be either.

383/400 can be either.

440 is always large (except '78)

Hemi is always small (with 7/16" drive bolts.

awesome. thanks guys.

i beg to differ about the statement "440 is always large (except '78)"

the truth is that ANY big block that was originally equipped with the lockup version of the 727 transmission will have the SMALL flexplate. the rest of them will most likely have the large plate unless the flexplate and/or converter has been changed. the hemi engine i wont address, as you arent likely to see one of them. small block engines i wont guess at either, although all of them i have had (2 318's and 2 360's) had the large flexplates. when i needed a small flexplate, it was $10 at the local junkyard. it was already off the engine.