What is the difference between the 642-1 and 642-2 as they look like the same gun? Is the dash 2 variant better?

The "dash" numbers indicate the same gun with some smallish engineering or design change. Some are truly minor and others are more significant.

You can find a chart, or at least an explanation of the difference by Googling.

It could be something like a different cylinder latch. Or omitting the barrel pin on some older guns. Just as examples.

642-1 = no lock
642-2 = lock

Ah I see thanks guys.