Both our 1.2 and 2.0 8v Nova's have GSi clocks, but neither have the oil pressure guage wired to anything. Seen this on Autovaux's comprehensive (if rather sloooow) website:
AVEL111 Switch - Oil Pressure £26.95
AVEL82 Switch - Oil Pressure £2.95
I'm guessing (hoping) the expensive one is for proper oil pressure, and the cheap one is the standard switch for the dash light? Is the hole and thread size the same?