Ok, now that we've established that a 55 to whatever truck pumpkin will bolt into your stock axle housing. You can get new ring and pinions for this later truck 'OPEN' drive from Patrick's, not sure of the ratios. Infact check with Patrick's for all needed parts for this job like, spring perches shocks etc. Afterall it's only money!

Jim, I.I. #173
(It's easier to get forgiveness than permission!)