If/when a motor in a FD gives up the ghost is it better to just rebuild it or replace it with something else? Could someone give me just a ball park estimate an a rebuilt 13b vs a 20b swap vs LS1(sorry dont hate I'd rather have a rotary but it seems simpler)

 

There are two subforums for you to check out:

-20B Forum
-Other Engine Conversions

Those should give you some ideas on what is required for an engine swap.