Several points to think about, you need to measure the input shaft length of the new Trans and compare to what is there now. I think truck Bell housings are 1" deeper than pass car (anyone know for sure?)  Also there was a change in bolt pattern on the bell housing at some point along about '65. Also know what your current input and output splines are.  Finally the trany might be different length. Best look at yours real carefully and then look at the one for sale.  BTW a t86 isn't that strong and the OD is the smaller R 10 OD.  If you can find a Ford T 85 OD; it is stronger and the OD is also better.