I just searched through my data sheet and I don't see anything specific to the 877A.
Huh? I thought the PIC16F877A Datasheet is ENTIRELY DEVOTED to the PIC16F877A!!!

Look at the section on Comparators (section 12), look at the Voltage Reference Module (section 13).

Datasheet=Dowloaded from Microchip
Datasheet 877A < > Datasheet 877
Datasheet < > PBP Manual

adcon1=7 is essentially the same as ADCON1 = 1110 right?
Ugh.... no.

adcon1=7 is the same as ADCON1=%00000111... note the % in the statement specified BINARY, whilst the absence of anything implies DECIMAL.

ADCON1=1110 is the same as ADCON1=%10001010110... now you might find that the ADCON1 register just doesn't have that many bits...

I am not a complete loser am I?
I don't know you well enough to validate that statement! But hey, we've all been there sometime.