If that thing really is capable of 1080i then it's going to upscale your 240p/15kHz input. It might look ok, but it won't look as nice as an older, curved 15kHZ only model - a standard definition model, in other words. A big old panasonic, NEC, mitsubishi or JVC might be a better bet, will be cheaper, and will also have a simpler chassis to work on when it comes to repairs. And will probably fit your gimbal better.
Upscaling also adds a bit of lag - you might not notice, but then again you might. I would suggest getting the monitor working and set up and first and trying a few games on it before buying, building or modifying anything else. What were you planning to run games from? A PC, a console, a multiboard like a Pandora, original hardware? And how were you planning to connect it to the CRT?