with 371 and down all gears will fit,3.7i and up  you need a different carer,purchase my 371 from amazon,had to machine the bearing surfice to use correct cups(older 44s used smaller . spyders and axel  gears worked( 4.11 is down 3.50 is up) i found this confusing but gear guy sorted me out

If I drove my current TBird like I drove when I was 16, I could destroy a 9" rear!      Seriously, I drive my car conservatively.  I've destroyed enough manual three speed transmissions to know better.  If I was going to drag race my car, I would swap in a 9" and a modern gear box.  The only racing I do now is to the ice cream store.

I was somewhat concerned about my 19-spline axles being the weakest link. However, if Phil has 4.11s and a manual transmission, I should have no worries with 2.72 gears behind a C4. It's my understanding that numerically low ratios are harder on the transmission, but numerically low gears are harder on the rear end. 

I imagine as an adult with an automatic trans the 8 inch should be plenty strong.  As an 18 yr old with a 64 Falcon, lightly modified 289 with a T-10, I did manage to destroy the OE 8 inch, 3.25 open.  The housing came apart around the rear pinion bearing.  Kind of a fan of 8.8s now, got one for my F100 with 3.9 limited slip and disc brakes from the local pick n pull for around $150.

Don

In the seventies, we ran a1965 Mustang convertible drag car.  I bought the body with no title from a junk yard for $350.   It had a 289, a modified C4 with a high stall converter, an 8" rear with small slicks and slapper bars.   At the time, the car ran in the 13s.  We never broke the 8" rear.

My cousin-in-law's 65 Mustang has the original 8" axle, but he had 3.50 gears installed. The 302 engine is producing about 300 hp at the crank, running through the original C4 transmission. The only complaint he has is that he wishes he had retained the original gearing for the highway. I think that all 260/289/302 Mustangs, with the exception of K-Code and Boss 302, used the 8" until the 80s Fox-bodied 5.0s were equipped with the 8.8" axle. K-code and Boss 302 were equipped with the Ford 9" rear axle. Depending on what you have under the hood, the 8" should be fine. It also should  be easier to service than the Dana 44.

In retrospect I should have used the Dana 44 instead of the Maverick 8”. I had to relocate the Maverick spring perches to make it fit.  

FYI: There are two different carriers for the Dana 44. The small carrier is for ratios up to 3.73. 

I have a dana 44 that came out of a 56 Ford wagon 6 cylinder with od trans  4.27 gears  Carl

My 55 T-bird's Dana 44 3.31 gears were replaced with 2.72 gears. The shop gave no indication that it was a difficult swap, although an Auburn limited-slip was also installed at the same time.