before i start swapping engines and moving things round id figure i ask here....im taking a 401 ((very very mild) thats bolted to a th400 out of one of our gremlins and putting in a pretty decent 360 that was bolted to a tf....is it possible to just swap flexplates?....NO – They will bolt up but are balanced for each size motor.
 
if not can the 360 flexplate be drilled to the th400...YES – Because the TH400 flex is weak (3 spokes)and crack the get replaced with a TF flex (for the size motor)and drilled to fit the TH400 converter.
 
then that 401 in going into the street gremlin with a tf....To do this you will need to buy a TF flex for a 401, remember the motor size/balance thing.
 
The other thing to know is the crank that is bolted to the TH400 trany now has a thin ring spacer in the end because the TH400 convert snout is smaller in dia. Than the TF converter snout dia. This ring needs to be pulled if it is to be bolted to the TF trany. And as you guessed the motor being bolted to the TH400 will need this ring installed. BTW they can be a bear to get out of the crank and I don’t know where you can get new as they are “hens teeth”.
 
im not swapping trannys due to the fact that the 400 is set up for drag and the tf isnt....plus lines are run and so on....uggghh im getting a migriane just thinking of it ...hahah...thanks in advance  
brian
And that is how it is done.
Dave ----

well i did put a 360 flex plate on a 401   year was a 72 have not had any problems at all  the 401 came out of a jeep with a 400