A lot of people recommend a 'dry build' as you suggested - that is build it to make sure all the parts are present and accounted for, then strip, chrome/cad plate/powdercoat etc and rebuild. personally i havent got the patience and just restore the parts and piece them together until i find im missing something. the dry build is good because it means not risking destroying any gooed-up gaskets
i dont know how much you know about restoring engines, so ill probably sound a bit patronising, but some pointers i can give are:
make sure you clean the sludge-traps - too many people dont bother and end up wondering why the big-end decided to throw itself through the crankcase
micrometer all the neccessaries such as crank journals, pistons/bores, crankshaft bearings etc and if it needs to be reground/built-up/sleeved/replaced, do it now while the engines apart - it beats having trouble when its a runner
replace the big-end shells and nuts, and if you can, the big end bolts. again, even if there isnt much wear, it may as well be done whilst its all stripped
the good thing about old british bikes is that most (if not all) of the roller/ball bearings are proprietary units, so just take the old one to a bearing shop and they should have the same one - also goes for rubber seals. so theres no need to buy one for 3x more than its worth because it has 'norton' or 'norvil' on the packet
it can sometimes be worth updating the bike with parts from later models - in this instance id investigate using a commando cush-drive rear hub and tls front brake (although the sls norton brakes are good enough). as good as it is to use the original bits, the benefit of restoration is being able to obviate the 'trouble spots' of the model, for example you could use a belt-drive conversion so the pressed-steel chaincases wont leak and you'll have a better clutch. also the AMC gearboxes can be a bit fragile, but you can no doubt get new stronger clusters and bearings
and as Goldy wrote, label every nut and bolt no matter how tiresome and trivial or atleast take a lot of photos - you'll thank yourself for it down the track
anyway, all that being said ... extensively ... have fun! it can be frustrating and slow sometimes, but itll all be worth it come summer
Hope this essay helps,
Blue