Assume your truck has the OEM TH350 and it will be the short shaft. Make some assumptions on $: Rebuilt TH350=$750. TH200 4R=$1500. So you only have to recover $750 and in enjoyment and driveability that is easy to justify. TH 200 4R is same overall length as TH350 short tail. Uses same driveshaft. Only have to move crossmember back to TH400 position... Here are some links I found on a Google search. Remember, buyer beware when it comes to auto transmission rebuilders... Pick one with a good reputation for warranty issues.
I’m planning on puttin an Extreme Automatics in my short step with a 427, but that’s going to be a $3000 trans...
https://www.monstertransmission.com/...E#.XAqIV4pMGhA
https://www.jegs.com/i/JEGS/555/6030...SABEgIsN_D_BwE
http://extremeautomatics.com/th2004R.php