Welcome to the forum!! As far as I know, no 4th gen Monte came with a factory moon roof. The options were hard top or T-top. I'd take it to a shop in your area that does aftermarket moonroof installs and such and ask them what your options are.
~ Matt H.
1988 Monte Carlo SS w/ T-tops, White with gray int, 350, Summit cam, World Torquer S/R heads, Holley St. Dominator intake, Edelbrock 600cfm carb, Champion 3-row alum radiator, ramchargers, 200-r4 with CK Shift Kit, billet servo, 2200 stall, Afterburner headers, Pypes 2.5" with x-pipe, Violator mufflers (stock exit), S10 front brake swap.