I've never heard of a production Maserati with Lucas FI using a mechanical fuel pump. Original equipment for these cars (3500GTi, Sebring, and Mistral) was an immersible Lucas electric pump in the fuel tank. The fuel metering system was mechanically driven off of the center of the right camshaft, so that may be what you are thinking of.
The only FI system I can think of that used a belt or chain driven pump would be the old Hilborn / Kinsler / Enderle design, generally seen on American engines in vintage hot rods, dragsters, and sprint cars. An interesting but comparatively crude system, it was reknowned for maximum performance, but not efficiency or flexibility.
Cheers,
Doug in Boise, Idaho USA