Chevy used a 15,000 2 speed rear in their 60 series during 60's until the 70's which had vacuum shift. Their 70 and 80 series used an Eaton 18k 2 speed which could be either electric shift or air shift. The air and electric shift were interchangeable. And these shifters were interchangeable from the 40's until the 80's when they went to an electronic shifter. Dana made a kit to retrofit the earlier electric to the later electronic shift. This is a service manual for the Eaton shifters.
http://www2.dana.com/pdf/AXSM-0029.pdfI know the earlier corporate 2 speeds were vacuum and nothing would fit from an Eaton. I don't think the later corporate will accept an electric shifter either. The shifters for Eaton are all the same whether they came from a Ford, IH or Chev except that from the mid 50's back the motors were 6 volt and the later ones had 12 volt. All I would know to do is take a shift unit from any old electric shift axle and try it. But I really doubt if it will fit. If you take the 2 bolts holding the shifter on and photograph what kind of shift fork sticks out of the carrier housing, I can probably tell by looking at it if an Eaton shifter will work.
If it won't run over 45, you aren't stepping on the gas hard enough. A 292 6 is rated at 4000 RPM a 327 is rated at 4400 RPM.
