After sleeping on it...

The TR-1A may have been a prototype. It output the 120kHz bursts rather than the data envelope as the TR-2A does.

50Hz should not be a problem for RX since you are only interested in the 120kHz burst that immediately follows ZC. But, I have never tried XIN so cannot offer anything meaningful.

If this is a one-off project, I would suggest a different chip. The ZBasic ZX328n sells for $10 plus the cost of the interface board and parts kit (plus shipping from the USA) but it has built-in low level interrupt driven X10 routines operating in the background. It has a serial bootloader making it easier to develop your program.

If it's a commercial project, I'd follow Anand's advice.