[BornInAFord]

Is there any difference between t5 crossmembers for 65-66 stangs versus 67-68's? I ask this because there is a conversion + box nice and cheap in my area complete with crossmember

IIRC, 65-66's have integral parking brake bracket on the crossmember, 67-68's mounted elsewhere.
I think otherwise the kits are basically the same or you can make them fit. Good luck!
Daniel