Big mistake! I forgot Prakticas (screw mount) among the camera bodies using the PX 625 (the metering is "by zero volt").I didn't find anything about the Canon FTb, bu on: Rokkorfiles.com a very interesting article, giving an easy job to alter the SRT101, this assembly should be possible to apply almost identically on many cameras.
This is pretty nice, all this hype, but would your old lghtmeter be even if you just tried it with an original battery?