Heavy Metal Alfa is right. I paid a little less than that price for mine last winter for a nice, very well documented car, with lots of very good and rare spares. My car scored 93.3 at the AROC concours this July, and Heavy Metal Alfa can speak to the good condition of my car, having ridden in it at the Convention.
The water pump is a big deal on these cars. Most of the time, it is an "engine out" job, though some people claim to have been able to do it by taking apart the grille and jacking the engine up a couple of inches to access it form the front. The other issues sound relatively minor (including the running on 6 cyl - what you need is a good SPICA guy: it is probably way out of adjustment, needing a new T/A and running extremely rich - my GTV was like this when I bought it and with Wes Ingram's book I was able to bring it back to spec. The Montreal is a little more intimidating, but it is unlikely that the pump is bad. There are lots of good resources out there, and Wes is good with the 8 cylinder pumps, too).
Problem is, they're really asking top dollar for a good driver, and it is unlikely that you'll be able to negotiate them down enough to make this one worth while. My previous owner had the water pump bearing replaced (allegedly without the engine out) and, together with some minor regular service, his invoice came to just under $3K, after a $1K courtesy discount, as he is a collector who sent all his toy car work to the same mechanic. With the kind of issues that you're talking about, plus the fact that you're unlikely to get any kind of history or documentation on the car from a dealer, I wouldn't touch it for anything over $27-28K, and even then, I would have to be absolutely satisfied that I wouldn't be finding any surprises (brakes, ancillary systems, rust) down the road, and that every single piece of trim (interior and exterior) was there, since a lot of this stuff is unobtainium now. Some Montreal parts are a lot harder to get than other 105 series cars (and you often have to go to European suppliers) and not so many mechanics on this side of the pond are familar with the Alfa V-8. A cheap Montreal is really not very cheap at all, and of all the Alfas, "buy the best you can find" applies the most to it.
The good news is, they do come up for sale (including some really good cars)reasonably often. There was one advertised at the AROC Convention recently which looked like a near no.1 condition. At any given time, there are several for sale in Europe, and good to very good cars are trading there these days in the $40K range regularly. Visit the website mentionned in an earlier poster's post, and buy Bruce Taylor's book (it is an absolutely invaluable resource, without which I would not have bought my Montreal).
Good luck!