5 speed trans swap into 1968 C-20 V8?

[drumdrew]

     I just inherited a '68 C-20 with stock 307 4-speed and only 73000 actual miles.  I have driven it many times in the past but haven't crawled under to get the rear end ratio but it is the GM diff rather than Dana.  I plan to do a mild build on the engine and probably add EFI.  I would like to upgrade to T-5 tranny, to improve mileage, if this is a reasonable swap but am really unsure of what I may need.  I am fortunate to have a salvage yard, close by,  that specializes in '54-'90 GM trucks so parts availability should be good.

     I know the T-5 has been a great box for performance applications in the 70's and 80's but am unsure if it is a good fit for a truck that still pulls a trailer once in a while? 

 

     I know many of you would just say dump the 307 for a 350 and move on but I want to keep the original engine as much as possible.  Any great guru wisdom on this swap would be appreciated.

 

  

Edited May 26, 2022 by drumdrew
left out important info