Joergen
First a few questions:
1 Most importantly why do you want to change the axle ratio , is this just to decrease the revs while touring? The 5th gear does this for you anyway, so dropping 2 ratios down to 3.07 will certainly affect this. Agreed if you revert to a Moss Box (for originality?) then a lower axle ratio might help , but dropping two ratios from 3.58 through 3.23 to 3.07 is quite drastic.
2 The gearbox has been modified in your car , have their been any engine mods ? Is the axle a Salisbury , or has it been replaced with a later Dana Spicer? What tyre sizes are you running?
3 With a higher power engine you would be able to get away with this , with a standard 3.5 on carbs it might struggle. I have a 3.9 which develops about 250bhp and my 3.23 axle is pretty good for touring , giving 25 mph per 1000 rpm on 205/60 x 15 tyres. I would not want to go much lower than this as I would lose acceleration.
I would need to look at some graphs of revs/mile but would need tyre sizes etc to be able to do the calculations accurately.
