Thanks all for your detailed replies. I decided to get an exact replacement (old 2.0 revision) to avoid any risk of complications when using with the old processor (I don't recall what version the proc. is.)

I'll follow-up post after I install to give everyone a data-point on this type of scenario.

One other question: does replacing the backup battery in the processor unit require re-programming the system, or does it have like a 30 second or couple-minute backup capacitor that will save programming during the short duration of a battery change? Where do I get a replacement battery for the processor?