I did my 3 spd with the kit from cool cruisers. Here are some lessons learned.
Use some sort of tacky grease to hold the needle bearings in the idler gear.
When installing the needles, do one whole circle, put the little spacer in, and then gently push it all in until you have enough room for the second row. I used the middle spacer for this. After you have one end done you can do the other, don't forget to put in the middle spacer! Use a deep well socket to push in your first row. I put my cut down shaft (see below) in the first end that I did to keep everything held together. It is a little trick holding it all together, but not bad.
The manual calls for a special tool to install the idler shaft, I cut down the old shaft and used that. I suppose you could use a wooden dowel if you could find one the right size. Using some sort of guide is very important, if you just try to shove the shaft in there you will knock a bearing loose and have to start all over again.
I thought the hardest part was installing the idler shaft. It would really help if you could get a buddy to hold the idler gear in while you knock the shaft in. If you do have a friend help you , you can make sure that you get the thrust washers lined up before you put the shaft in. I did this by myself so I had to hold the gear with one hand, start the shaft and then tap it in, way hard
One thing you will want to be careful of is the woodruf key slot on the end of the shaft. It is not very thick and if you hit the shaft on that side with the hammer it will break off and you will have to get another one.
One trick to reinstalling the bearings is to heat them in the oven, not real hot, just about boiling. Also freeze your shaft, not for long, just about an hour. The idea here is to contract one, while expanding the other, and they slip right together and become a tight fit at the same temp. This sounds drastic, but it isn't as long as your temp differences are not too high. If you put your bearing in the oven and broil it and freeze your shaft over night, one of them will probably crack when they expand/contract.
PM me if you need a copy of this part of the service manual.