I think either way you choose to go is going to call for a welder.
You can do as George said 55-62 3rd member,chunk,pumpkin everyone call it a different name and install in your original rear end housing. 3rd member
This will be a good time to install new bearings if it needs them(axle,differential).You will use your original axles that you have.You will need to set the pinion angle and weld up the pivot points on the rear end solid. pivot points
Try to get all of the rubber bushing out of the pivot area,it will catch fire and melt and drip all over.

I put a 58 pumpkin in my 1951 suburban rear end with a 3:90 gear set,coupled to a t5 transmission.
Here is a link to some pictures I took of my conversion. conversion pictures
I extended the splines,shortened the collar and pilot shaft area.I also used a 1/2" drill bit to open up the transmission mounting bolt holes. t5 conversion



Tim

1951 3100 Chevrolet
1951 Chevrolet Suburban Carryall
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