Stop in for a cup of coffee

My '69? A 727 with 3500 stall and a manual reverse pattern valve body.
then you would just need the 08 and older ECMs. theres a spacer plate sold by mancini for 125 to set the trans back 1/4 inch or so for the extended flexplate but otherwise, its a dead straight bolt up. Depending on how much you can source a running motor for, you could do it cheap enough that I bet selling that 500 hp monster would offset 90% of the cost.