['ol Pinion head]

The axle housing dimensions are the same on all '77-'96 Chevrolet B-bodies (Chevrolet Caprice's and impala's) I've measured. Don't have any 90's era Hollander books to double ck, but are the '90"s B series wagon rears any wider than 90's B series sedan rears?
I've pulled quite a few 8.5 B series rears of this vintage & torn apart quite a few 8 7/8 in mid 80'sBuicks & Caddys & don't believe they are any wider, I in fact believe they are the same width rear. That would make them all too narrow to fit in a '65-70 B series Pontiac.

Once one starts comparing the below rears, they are basically the same axle flange to axle flange & as far as the geometry goes with the upper control arm perches. There are different styles of housing ends, 28 spline or 30 spline axles, different looking spring mounting tabs, Spicer 1310 & 3R pinion flanges & theyre were two different factory rear disc brake set-ups (the '77-78 LeSabre Sports Coupe version & the '90 Caprice version).

GM rears:

'73-77 A-body 8.5 c-clip
'73-77 A-body 8.5 bolt-in axle (one of my favorites)
'77-78? B-body 8.5 bolt-in axle (same as next above)
'77-78? B-body 8.5 c-clip (Palla cop cars of these years will have usually have 8.5's)
'77-mid 80's 7.5 c-clip B series (weak junk)
'77-84 B series 8 7/8" MP series c-clip
mid 80's- 96 B-Body 8.5 c-clip (30 spline '88 & later)

Another style of GM rear that is wider than the '73-77 A-body/'77-96 B-body rear AND the upper control arm perchs may be very close in geometry to the 65-70 B series PONTIAC is the '71-76 GM B series rears. Know these are not a direct bolt-in to '65-66 B series Pontiacs, as I've built them all, but could be something to ck out to see if upper control arm perchs have the same spread & same geometry. If they do, its as simple as removing lower control arm/shock perchs & correctly positioning & welding the the early Pontiac style on.

Of these GM 71-76 B series rears:
-'71+ 2 door & 4 door Chevy Impallas & Caprices typically had the 8.5 C-clip axle rear. Also were used in some low horse '71- (maybe) '72 Pontiac Catalina's
- 455 equipped '71- Pontiac B series & often Olds Delta 98's of these years had the 8 7/8 MP series rear (some manuals may refer to it as a 8.75).
-Biggest '71-73 Buicks with 455's typically had a 9 3/8 which is also very hard to find good ratio posi & gears for. 3.42's in this style are real tough!

Good luck, as I'm out yarding I will try & get some detailed pics. I have nothing anymore for '65-70 B series Pontiac rears in my racks. Just sold the last of my '65-70 P series axles (with new axle bearings installed).