SB to 383 in original BB car

I have a 69 GTS 383/auto convertible that has had a hard damn life. In the 70's, it caught fire and got a small block swapped into it, so it still has a SB K frame at the moment. I intend to use the Schumacher mounts to put a 383 back in, but i was wondering if it would be possible to keep the PS that had gone in with the SB. I heard that the BB cars didn't come with PS, but could they have PB? I have no build sheet and the fender tag was lost long ago, so unless someone has a Hail Mary pass for me, I guess i get to take some sort of creative liberty as to what it was equipped with, although i would love to return it to stock.