To complete the system I would swap out the dual scan "cs" display for an active matrix "c" one. I did that with my 1400 and the improvement is stunning. Stupidly I never put a bid on a G3 upgrade that was on eBay UK about a year ago and it sold for very little.
However, there is such a thing as upgrading a machine too much and as Quadraman said, for that kind of money you could get yourself a decent Pismo with generally better specs.
I personally wouldn't pay that much for a 1400, but it is a damn sweet machine, minus the crappy cs display. My PB1400, while nowhere near as loaded, has a active matrix display, and it is simply beautiful.
64MB is a bit small to get the most out of the G3.
I can't stand DS LCDs one of my Wallstreets had the 800x600 DS and I replaced it with a 14" TFT (much better) from my spare parts pile.
If I had a 1400c I would probably just leave it as is instead of putting a G3 in it. Sometimes for the money you are better off just getting a newer machine unless the older model means something special to you (or the upgrade is $20 or less).