My Spyder came with a 3.88 r&p and a .82 4th which would have created that big gap between 3rd and 4th, which is why I changed the gears to a 3.44 and a .93.
That's what I run in the TD as well and it works a treat: 1st is plenty low for starting off on hills and she gets up and goes just fine. Probably hits 60 in about 6 seconds flat at the top of second gear. I'm sure the 3.88 would be quicker off the line but I didn't build her to drag race.
The 2.2 Subaru, with 140 ft-lbs and 135 hp, loves this trans in Bridget, which weighs about 1800 pounds. 6000 rpm in 3rd is 100 mph (theoretically, of course); 3000 rpm in 4th is about 70 mph and that's the sweet spot for keeping up with highway traffic, even if I'd rather be doing 50 mph on a shaded two-lane.
I'm thinking the same gears should work just about as well in a 1400 (or so)-pound Spyder pushed by a 120 hp 1915. Same red line as the Suby (they both peak about 5500 and pull through 6000). The Spyder's power-to-weight will be a little better, with each horse moving a little under 12 pounds, as opposed to a little more than 13 pounds in Bridget.
Picking the Spyder's transaxle up next Saturday, and progress continues.