just picked up a 1942 dodge 1/2 ton truck. how much modification is needed to install a 8 3/4 rear out of a 69 b-body ?

if it has leaf springs you will probably need to move the spring perches on the axel housing. if it has the skinny leaf springs(my 47 Desoto does) the only place I found the narrow perches was at tractor supply, in the trailer parts section.

Depending on what it came from, you will likely need to have the rearend housing narrowed and axles cut and re-splined. Thats what I did with my 37 P/U. I would guess your track width is about the same.

i measured the rear end in the truck and measured the b-body 8 3/4". the 8 3/4 is actually 1" shorter than the truck rear measuring from backing plate to backing plate.

the correct place to measure would be the axle flanges--where the wheel mounts on the studs----to many variables on backing plate offset or drum widths...

71-74 Mopar "B" body, 68-74 "C" body, and 66-74 truck all use the same 8 4/3 rear axle housing, only the perches are positioned differently. Any difference in the backing plate width is due to which brakes were used.

All "A" body, all 70-74 "E" body, all 66-70 "B" body, and all vans ("A" & "B: vans had different axles as well) used different 8 3/4 axle housings. Not counting any of the earlier tapper axle vehicles.
From narrowest to the widest:
"A" body (also small 5 on 4" bolt pattern)
66-70 "B" body (some think there was a difference between those 66-68 and those 69 & 70, but I believe the difference was in backing plate width & brakes)
"A" Van
70-74 "E" Body
71-74 "B", 66-74 "C", 66-74 truck
"B: van (also off set)
Gene

We put an 8 3/4 from a 68-70 charger in my dad's '40 pickup. Didn't even have to move the perches if I remember correctly.

I put a '78 D100 8.25 in mine. It bolted in with the shock mounts from the '78 and new U bolts of course.

49 plymouth coupe here...
used a 68 B wagon 8.75 in mine. Had to weld on new perches. Good width...

EDIT 40, not 49!

finished mounting my 1969 b-body 8 3/4 rear tonight.has 3:91 gears. made all new spring hangers and shock mounts. rear leafs from a 69 barracuda.since i had to re-position the spring hangers, i had to make new frame cross members. made out of 2 1/2" thick walled stock.

and here is a picture of the finished job. perfect width. i also lowered the rear by 2". i will be lowering the front end about 3" with a fatman mustang 11 front. next i'll get started on installing my late model 360 magnum w/904.

looks great