I've been reading up on the subject and now have a better appreciation of what I am going to be up against but as a marine engineer of many years experience nothing to phaze me.
I bought a copy of Paul Cangialosi's excellent book which has been very informative.
As I will be going from a 4.55 to a 3.55 diff at the same time I'm going for a slight change of ratios in the box so the input shaft and countershaft gears will be new anyway, I now have a better idea of what is worn out unlike when I did my first gearbox as a youngster!!
I'll keep in touch as I progress.
Graham

You're going for the overdrive conversion, aren't you?!
Done a few for others....it's a good compromise to going to a 5 speed...and still looks original.

Hi Joel, not so much an overdrive but i'm changing my diff from a 4.55 to a 3.55 so thought my 2.2 1st gear would be a bit tall so I think I'll go with Autogears M22w set up which gives 2.56/1.75/1.36/1.00 ratios.
I've seen the o/d gears offered but a bit puzzled as to how it's achieved as top is normally straight through 1:1?
I had considered going for a 5 speed but with shipping and customs it's just a bit too much.
Graham

Graham, the O/D set-up for the Muncies is a neat deal. It actually changes 3rd gear to an overdrive ratio, leaving 4th gear as is. You flip the lever on the side cover for the 3-4 shaft over, and it now goes from 1st, to 2nd normally, and when you shift into what was 3rd, it actually shifts the trans to 4th(direct), then the shift into what was 4th is now an overdrive ratio replacing 3rd. The kit changes the cluster gear, along with the 2nd and 3rd(O/D) gears on the mainshaft. The 2nd gear change is so there isn't such a large gap between the 2nd and 4th(now technically) 3rd gear ratios.  

I did wonder if that's how it's done a bit like a 3 speed and overdrive then. Graham

Took the box out last night and not a pretty sight, only half a key left in the 3/4 synchro hub so no wonder it had a bit of a crunch! the 1/2 hub is very loose and sloppy and the engagement teeth are a bit rounded so even if I wasn't changing the ratios they'd need replacement anyway, will hopefully get it all in bits tonight and see what the reverse gear is like then should be ready to order the parts, side cover looks good just needs new seals, I haven't measured the forks yet but they don't look too bad, although I already have a new set.

I was looking at my shifter yesterday and with a bit of fettling I think it should be salvageable, I think there should be a bias spring to push the lever over towards the 3/4 gate? which is missing had a look at the assembly manual and couldn't find a drawing there, am I right?Graham 

Got my new clutch so that will go on first, when I removed the old one I found a needle roller spigot bearing, should I keep this or change it for the bronze bush supplied in the clutch kit?
Should get my gearbox parts in about a weeks time so will probably pulll my diff while I'm waiting.
Graham

As the needle roller spigot bearing was in good condition I left it in place only cleaned it and gave it a lick of fresh grease, so new clutch mounted, gave the aluminium housing a good clean and a fresh coat of orange engine paint while it was off, new rubber boot fitted around the clutch arm as the old one fell to bits so will put that back on next then should be getting my gearbox parts through in the next couple of days so can get on with putting it all back together.

Started building up the gearbox yesterday, all gears back in the box, just got to helicoil one of the mounting bolt holes on the tail housing before I put that back on and it's all ready to go back in.