Are you sure the 9 inch is 3.55 gears? Most of the 9 inch rears that I have dealt with in the past have been 3.50 gears. The 3.55 ratio was always an 8 inch and 8.8 inch rear end ratio.
It might be, I quickly glanced at it and when I measured to ratio it was about 3.5. I knew the 3.55 in 8" so I assumed it was the same.
Ahhh everyone is wimps these days(including me)... Back in 1969 Ford was selling Super Cobra Jet 428s with 3.91 & 4.30 gears plus warranties for 50K mi... With a 3:50 in mine and at the time also a 5-speed, 5.0 stang, I was always hunting for 5th gear... Real OEM Ford gears will be 3.50 whether 8" or 9"... Aftermarket 3.55 are available... If you go back to the first 9" in fifties there were 3.56 ratios...
In later years no doubt a possibility... I was looking at a 1969 Ford engine, transmission & rearend reference guide, not a 3.55 listed for any application... Not listed in the 1971 shop manuals either...
Will I would bother with getting a CUSTOM drive line made ... You can order a aluminum drive line with ujoints from Coleman Racing Products a whole cheaper than you can have one made . Order spec. are something like 35" to 60" in 1/2 " increment in different OD. for the same price . My son order one for his Falcon 3" od. 52.5" long for $272.00 ship to the door. The local drive line shop was OVER $400. plus joints
Why bother ? Any driveshaft for a Fox Body Stang will fit. Only difference would be the slip yoke spline and diameter. I'm running a stock 2004 shaft I bought new on Ebay that was a left over from production. I don't recall, but total cost was around 100-200 dollars.
I was going to say the same thing. I'm running a 3.50 geared Nine from an 81 Bronco in my Comet. And to the OP, the rpms running down the freeway aren't that bad. With 26.5 tires it turns around 3 grand at 70. And depending on the engine build, that can be a plus in the mileage department, putting it in the powerband where the engine is the most efficient. Mine gets around 18 mpg at this rpm.
