My method of choice is leaving the manifold in place and removing instead the cruise actuator.

I don't think removing the manifold is optional if you're going to ream the prechambers.

Get a long 6mm hex bit with a ball end for the back 3 intake manifold runners.

Have a new gasket ready but I'd reuse the old one if it's intact since manifold vacuum is not an issue. There's also a gasket between the crossover pipe and intake manifold. Another one I reuse. Keep a rag under this smaller gasket as you remove the crossover pipe because the gasket can slip between the block and IP.

Decide if you're going to do anything about the soot lining the crossover pipe and manifold. It takes chemicals and scouring to get it clean. You probably won't notice any performance enhancement for the effort.

Good time to check that all the injector line clips are in place.

Sixto
87 300D