I'm still researching this SAG 3 to Muncie 4 swap. All indications are that it is a direct bolt in swap...with one possible exception. I found one source that says the SAG bearing retainer is 4 10/16" ø, while the Muncie is 4 11/16" ø. If this is right that ain't gonna work. The spines are the same at 1 1/8"ø 10/27 (earlier Muncies). The input shaft length match at 6½". The pilot diameters are .590". The pilot length is 1".

So Neill your warning is well taken. The bearing retainers have to be the same diameter. Maybe I have to find another bellhousing. I'll keep researching.