For the sake of a couple of hours work, I can swap out the diff gears quite easily. I'll give the 3.54 a shot and if I don't like it the 3.77's there to go back in
 

It probably sounds close.. keep in mind the speedo was possibly out a touch (so in reality was slightly less than 100kph). It used to rev to about 7000 but I kept redline at 6500.
If you have the 3.7 id be putting that in first.

Quick update.
3.54 is in with the 5 speed.
1st gear is still too short! I think the best set up would be 3.77 with 2.98 1st gear.
3.54 still good and makes the most of the torque especially with my 38DG*S.
You just really have to watch what gear you're in at certain revs. 3.54 has made the motor hungry for redline, which you need to hit anyway for when the revs drop after gear changes. The best thing about it is when you back off, the car doesn't want to come to a halt like it did with 4.125! 
Cheers
 

3.77 is back in. Even with the mild cam, I found it too easy to drop below usable RPM's with the 3.54. Lack of grunt &  205/60/13 tyres adding to the problem :D
 
All good now though, zips through the rev range perfectly.
 
 

Type 9's are renowned for having a short first and big jump to second, this is probably where you are loosing time in accelaration, im a pomme and have built kitcars and always played with cars with these boxes in. When I was a teen in uk cossie replica's were the thing to have but the gearbox still drove you mad when you wanted to go quick. A lot of friends played with various diffs etc, which improved (or masked) the problem. Before I left uk a friend changed the first/ second cluster from burtons if I recall, it really transformed the car, then he played with diffs, wheel size etc and made it into a real flying machine!

Hey Graham
Yes that's all I've done- masked the problem. 2.98 first gear would be fantastic.