The advantage of a oscilloscope-type CRT-based display is that you'll usually have a vertical gain or 'height' control you can twiddle to adjust the aspect ratio. But a 625 TV or monitor is fixed unless it's very very old (1950s). Switching crystals in the converter could be done with a very small relay to keep the crystal-chip lead lengths to a minimum controlled by a front-panel switch.
An alternative is to use something like QRP Labs 'Progrock' kit (
http://www.qrp-labs.com/progrock.html) but it could be viewed as a sledgehammer to crack a nut. Very useful for other things though. The GPS discipline is optional, not essential.
The two different line rates, US 15Hz/EU 16.7Hz, are dealt with a sample-rate adjustment front-panel pot. This could be also a way of overcoming this problem by setting the sample rate such that only 120 samples are taken in a 120-line picture (It is actually 240). The remaining ones would be in within the sync-pulse and ignored.
It's something that I'll put on the 'back burner' for the time being, the rest of it requires my attention right now.
Interesting site Harry, shame some of the links are dead. 80 TTL chips, nothing unusual in those days - keeps you toasty warm on those frosty mornings.
Steve A.