While not ideal, I did it. My oil pressure had been dropping some on a fairly new rebuild, and when I was yanking out the econo roller cam (as a preventative measure), I noticed a fair amount of wear to the #1 bearing, as seen here:
http://pages.prodigy.net/buickv6/_images/cam brg wear 1.jpg
I didn't think I had anything to worry about with the rest of the engine, so I bought the very nice cam bearings from TA Perf just to get the #1 bearing (at the time, and maybe still, you had to get the whole set, even if you just wanted the #1.)
S10xGN on this board has a cam bearing installation tool he fabricated, and he was nice enough to loan this to me. I used this to drive the old bearing out. It dropped down on top of the rods and crank and I fished it out from below since I had the pan off anyway. Then used the tool to drive the new one in. Took me a while to get it right, never done that particular job before, it took me a fair bit to get it going in straight. But once I got it started, it was a piece of cake.
Oil pressure came back and has stayed with me so far, I'm pleased. I understand the stock GM bearings are fairly hard and a good choice. The typical aftermarket replacement bearings are babbitt bearings and are too soft, they will wear fast and are best avoided. This is apparently what the machine shop installed in my block. TA Perf bearings are aluminum and harder than stock and a great choice. Federal Mogul (I think?) has some teflon coated cam bearings, I don't know if those are good or not. I know a few guys have used them, but I've never heard any reports on their durability.
Conclusion: you have to have the right tool, the tool is an expensive purchase for a one time job, but the job itself isn't too bad.
John
