SJ410 5 speed gearbox

I am thinking of changing my Mk 1 4 speed gearbox for a 5 speed type. I know there is usually problems with pulling power in 5th but my Suzy is fitted with 4.55 to 1 final drive from an LJ so I do not think I will have the same problems. The reason for fitting the 5 speed unit is to up top gear for motorway(freeway) driving as at pressent she is reving at 4500 rpm and only doing 50 miles per hour. Does anyone know which are the weak components in the 5 speed box and the ratios. Thanks for any information it would be very useful.
Dieselman73 England

Gordon,
pre- late '89 ratios are, (from the info. posted on "Suzuki FAQ" site).

1st 3.65
2nd 1.95
3rd 1.42
4th 1.00
5th 0.79

Just finished a rebuild of the 5 sp in my son's Samurai, the first one I've done of these little beauties. I'm used to rebuilding the heavier transmissions in my collection of old Jags and I must say, I'm impressed with the quality of the Samurai 5 sp. box. It looked like a very well designed unit to me, I particularly liked the idea of a gearbox that has no gaskets in it. Makes for a more precise fit of the bearings in the case. I found dismantling of the box to be very easy, no special tools except for a good quality. 2 leg gear puller that will reach to about 4".
The box we rebuilt had about 147,000km on it when we took it apart. no idea if the oil had been changed on a regular basis by PO's but we were very pleased to find that all the synchro components were in excellent condition and didn't require lapping or replacing of any parts at all. All the shafts' ground surfaces were all in excellent condition which was quite a pleasant surprise.
The parts that we found to be the most worn were the large and small caged needle roller bearings on the mainshaft and the deep groove, thrust bearing with snap ring ( NTN 6206NX9 ). This one was particularly bad and was probably the cause of gear noise.
As it was so easy to replace other bearings at the time, we also replaced the following ball bearings although the old ones were quite serviceable

1x NTN 6304
1x NTN 6305C3
1x NTN 62/28C3
The rear oilseal (Suzuki part) was cooked dry and leaked, couldn't source that anywhere but a Suzuki dealer but you should at least buy something from them now and then, right?
The front oilseal was fine but I replaced it anyway (Suzuki part). The throw-out bearing sounded a little rough but I crammed a bit of CV joint grease in it and it smartened up- put the bearing in a sandwich bag with some grease and just keep kneading it around for a while..
The white metal bearing surface in the tailcase was worn but we decided that at + $300 for the tailcase extension, we would go with the wear.
Recently noted a much cheaper way of replacing this bearing, it's posted on the Suzuki site that discusses after-market and interchangeable parts.

Hi AJM Thanks for the info. The SJ 410 5 speed gearbox is different from the 1300 Samurai box. Most of the Samurai's were built in Japan where the 5 speed SJ 410 Santana was built in Spain and I believe there is quite a differance in quality. Anyway thanks for the info. Gordon