Yep, go for the Museum kit
http://www.earlytelevision.org/405_modulator.html unless you like messing with RF. Looks like a decent enough design, though the IC is really for 525 TV with FM sound. I'd have just used a transistor. I've used the 1496, but it's overkill as you don't need a suppressed carrier.
But Jeffrey's right. You really need a monitor. Virtually all 405 TVs are "live" chassis, so to adapt a TV to a monitor you'd need an isolation transformer as well as change over switch and buffer at the video and audio detector diodes. I've converted plenty of 625 sets to be TV/Monitors. Straight forward if you have schematic and the isolation transformer.