Hey, nice looking bike! Cantis on an 83? Maybe that isn`t unusual, but it kind of surprises me. I may be nitpicking a little but here, but I don`t think your bike had the same frame as a 1000. I believe the 6xx frames were beefier than the 1000s- that could be a good thing or a bad thing, depending on your point of view, but either way you`ll have a nice bike.
I`d see first if you have enough brake adjustment for 700c wheels- if so, you`ll have more rim and tire options. If not, it ain`t the end of the world- still a pretty good supply of 27 inchers available. Yes, you`ll need to reset the rear triangle if you want to use a 8-10 speed hub, but that isn`t a big deal. Sheldon Brown explains exactly how to do it on his website (I did mine by his instructions), or you can have a shop do it. Probably not very expensive. If you want a different saddle and bars, I suggest test riding complete bikes that have the components you`re interrested in to get an idea how you like them. They still might catch you by surprise after several hours in the saddle as opposed to an hour or so on a test ride, but at least you`ll get some idea how they feel to you, personally.
As far as the rest of the bike goes, Imi has a nice built in mind for his. If you want to go that way, great, but you could pretty easilly cut the cost by a good margin by going from LX to Deore on the deraillers and/or looking for less expensive rims, tires, crankset. Eight speed costs a little less than nine speed, too. Also, if you want to do it a little at a time, you could most likely use your friction shifters (maybe even deraillers) with a cassette on a new set of wheels while you give your checkbook a breather. Never know- you might even find out you like that set up well enough to keep.
EDIT: By the way, I`m currently rebuilding a 91 roadbike using that "bit by bit" method. Very similar situation- I loved the frame, and all the parts were close enough, but I wanted to upgrade pretty much everything eventually. It isn`t exactly a cheap way to end up with the bike you want, but if it takes a few years to get around to all of it, so what? You`re riding in the mean time. It`s like buying you new toy on lay away and getting to play with it the whole time you`re making payments
.