Rear end swap ?'s

I've got a 69 mustang with a stock 8" rear and i need to swap that sucker out. I was looking at getting a 9", but i heard someone say an 8.8 out of a fox body mustang will work just as well, and they are a lot cheaper. I've looked around and he seems right, but im not sure if there are any fitment issues, or can it just bolt in? I'm pretty sure i would have to lengthen it, I believe the stock 8" on my car is 54" wide, but i haven't measured it. i dont want leaf springs im going with an air bar, and i want 4.11's with a locker. any help is awesome

What have you got under the hood. How much are you putting down. Come on we need more info.

I've got a 408w stroked w/ Coast high performance pro-street fighter http://coasthigh.com/Assemblies/Ford/ford_408w.htm
Edelbrock Vic. Jr intake,
demon 850
Tremec tko 600
AFR 205 race heads http://airflowresearch.com/205sbf_rh.php
Full Roller valve train with a Pretty big cam, It's been about a year since i built it and the cam specs have eluded me...Think its like .565 lift with 264* duration and 108 degree lobe centers..
The motor makes about (estimated, never had it on a dyno) 500 horsepower at the crank but i've got plans to go bigger. A rear end that would handle about 600 would be fine for me. I don't see any reason an 8.8 wouldnt, but i want to get some info before i just go out and get one.

Any more info ill be glad to tell

A 31 spline 8.8 would work just fine, but personally I'd go to a 33 spline just to play it safe. Strange makes a nice set of 33 spline street axels.

That is a lot of torque, if you plan on launching that sucker, you need 31s 8.8 or 9 will do fine. I would perfer to have a 9" myself, but that just me :)

Not sure about the '69 cars but I know it gets hard to set up a fox with a 9". The way they sit screws with the geometry.

Not sure about the '69 cars but I know it gets hard to set up a fox with a 9". The way they sit screws with the geometry.

That is why I would try to stick with the 9" for the older Stangs. Geometry can be tricky.

Down the road i think a 9" is something i want to go with, but for now i think my budget is better suited for an 8.8. I think i can find one with disc brakes for under $1000, I might have to lengthen/shorten it, im not sure what the length of most 8.8's are
Thanks for all the Input

Also, what's the deal on 4-lugs rears? Can they be converted to 5 lug with new axles, or is it just better to avoid the 4 lugs?