Having done a conversion on my 65 Vette from a SB to a 502 BB with a Keisler 5 speed tranny .. I also know what you can run into. When you change one thing it always effects another.
It took me a year including redoing the frame with all new suspension parts with the Body Off.
When you drop in a BB then Fuel Electrical and mechanical all jump up and bite you in the Hiney.
But being as ANAL as I am an you ..If I didn't have what I needed I either had it made or Fabbed it myself or bought the correct part to make it work.
Since all the parts are happy and work together I'v had no problems with any brakeage of any thing in the drive line. And I Jump on it every now and then... Mostly "Then"
Here's a pic of the motor cramed into the 65 Vette.