New to rear end swapping

[Michael James Adams]

Hello folks, so looking at a 742 casing rear which I believe is an A body rear, spring perch measurements are 43.5 from the looks of it and flange to flange right at 55. I want to swap it in my 1974 plymouth valiant 4 dr sedan. I know I'll be looking at shortening the drive shaft or getting an aftermarket but will I have to reset spring perches and do pinion angle? I was looking at shortening it and putting axles for bbp.
Thank you

 

[John Collins]

From research on this site and others, this is what I’ve learned. It’s a 68-70 b body rear end, which is 54 15/16” from flange to flange. You’ll need to move move the perch’s in from 44” to 43”, shorten it, shorten your drive shaft if you’re going from an 7 1/4 to 8 3/4, get a u joint adapter 7290-7260(Doctor Diff sells them), you’ll need new Ubolts and shock plates if you’re upgrading from an 7 1/4 and new yoke hardware as well. It will already have 5 on 4.5 BBP axles.

I’m currently upgrading mine now with a 65-67 b body rear. I don’t have to shorten my rear as it’s only a little bit wider than an A body rear and in my Dart Sport, the extra inch and change is an improvement on looks, in my opinion.

 

[Michael James Adams]

Awesome, yea further research shows its the b body rear. I see some people massage it to fit without shortening it but I rather shorten to get it perfect. Now can I have my guy just move the perches inward at the same angle? Or will the pinion have to be set no matter what.

 

[IfItsGotWheels]

Just move the perches in.

 

[DAndy ART]

Move the perches in to 42" and inboard the leaf springs with a Dr Diff kit.