Not sure.
In that thread it looks like you're using the external interrupts (INT0-INT2) but the 877A only has one "normal" external interrupt (INT0). However it does have four Interrupt on change pins (PortB.4-7) which you could use.

Or, like I said, you might get away with simply polling the inputs in a loop. As long as you read the inputs atleast ~120 times per second you shouldn't miss any pulses.

/Henrik.