The intake manifold has to come off to change out the oil pump. Yes it will fit. Its under the carb.
Take the nozzle off the pump then the nose cone, and the oil will come out. if there was a bunch of water in there it needs to be checked out. make sure to use a new OEM oring for the nose cone.
A LCD gauge can be swapped into any machine, but you will need to run a couple of wires and change some connectors in most cases.