Shelby Mustang - Transmission Question

Thinking of swapping my 64.5 289D Mustang to 4 speed. Shelby used BW T10 but most posts on net seem to prefer the Ford 4 speed toploader. Is there an advantage to either? Why did Shelby us the BWT10?

The 60s versions of the Top Loader had a cast iron case where as T10s switched to aluminum by the mid 60s so weight was probably a factor, also Shelby had already been using T10s in the Cobras so it may just have been a case of using a known commodity. The advantage of using a T10 now is that you can buy a new one for less than the price of a rebuilt Top Loader. If you are doing a conversion however I would look into one of the Tremec 5 spd kits as they have the advantage of over drive.