A 14bFF from a GM 1 ton pickup will have the same spring perch width as your 71 because the 1 tons used dualies which required the spring perches to be more inward for the springs to clear the inner dual wheel. Measure to be sure before purchase. So it comes down to the advantages of a 14bFF vs. an Eaton H052 rear axle:
14bFF advantages:
1. More ring & pinion gearing choices.
2. More locker choices.
3. Reasonably priced diff rebuild kits. Hub bearings no more costly than Eaton.
4. Drum brakes are superior size to Eaton's 2" wide shoes.
5. Strong, 30-spine axles. Can handle BB torque with aplomb.
14bFF disadvantages:
A. Heavy sucka! You'll feel that massive unsprung weight as a poor ride in back. Axle is tubes pressed into heavy cast pumpkin.
B. A bit expensive to buy, but can be found cheap ($1-200 not refurbished)
C. Shop R&P labor costs more to rebuild unless axle is off vehicle because of integral carrier.
D. IIRC, only GM 1 tons had 67-72 spring perch width.
Eaton H052 advantages:
1. Lightweight axle in comparison to 14bFF. Eaton housing is all welded mild steel. Retains reasonable ride characteristics.
2. Carrier housing is removeable. Makes R&P repair labor cheaper. Makes swaps easy.
3. Avaiable for a pittance thru most wrecking yards. This great axle is ignored by most 4 wheelers looking to upgrade their 1/2 ton.
4. IIRC, all pre-73 Eaton H052s' wms and spring perch width fit 67-72 K10/20s.
5. Axles have only 17-spline, but they are arguably as strong as 14bFF axles. Can handle BB torque with aplomb.
Eaton disadvantages:
A. Few ring & pinon choices, mostly thru used/wrecking yard market.
B. Diff rebuild kits costly. Main carrier bearings are expensive. Hub bearings comparable cost.
C. IIRC, only one locker choice: Detroit locker.
D. Drum shoes only 2" wide but within 12" drums. Drums are no longer available new, but I took D60 12" drums and had a brake shop turn the outer lip down to clear the Eaton's drum backing plate. Presto! New drums.
Eaton axles can use the 14bFF disc brake conversion brackets. Also, one can swap the side gears in an Eaton's Detroit locker with a 14bFF's Detroit locker side gears to run 14bFF axles in an Eaton.
Between the two, I'd go with an Eaton for the lighter weight as long as the R&P gearing matched your needs. Go with the 14bFF if you want a selectable locker (ARB, etc.) or need R&P gearing not available w/Eaton axle.
Another option is to use a D60 out of a 67-72 K20 pickup. Less weight than the 14bFF, plethora of gear & locker choices, can also be converted to disc brakes, axles can be upraded to 35-spline ($$), prolly more expensive to source, less common in wrecking yards. Ring gear size (9.5")[*Edit:9.75" Thanks JIMs70GMC & 1969 GMC) is inferior to Eaton & 14bFF (10.5")
For the front axle, use only a D44, if not a D60, for the superior parts & locker selection over a 10-bolt front. You can find front D44s with a 71's wms & spring perch width. Enjoy.
