The Olds one doesn't fit.
The Chevy one doesn't fit.
If you buy the Pontiac one from Glenwood, It fits great but the hoses will be pointing to the side! A Pontiac manifold has the bolts running fore/aft instead of crossways like most aftermarket chevys. The best way to do it is to just block off the thermostat hole with a plate, and use the two pipe tapped holes in the crossover. Or, just run one big outlet hose, it works fine.
DJ