I am a fellow motocross rider...never got the opportunity or had the money to race though. Do a compression test that will let you know the health of the motor. If it runs good then it should be good to go on the inside. I highly suggest getting a good honda manual for it...they are a little expensive but the information is far more accurate then some of the aftermarket manuals I have run across. Tune up has a list of items on the old 750's. Plugs, replace or at least clean the points....then set timing and dwell. adjust valves, adjust timing chain. The carb issue kind of concerns me...the choke is very simple so not sure why they coudn't get it to work. Get that figured out because they are kind of cold blooded especially if the jetting isn't right on with the pods. Carb sync is critical on these motors so I am suspect it is correct if they couldn't figure out the choke.
Cams do wake up the 750 but...you need to replace the rocker arms with a new cam and they are unavailable from Honda, so you have to send them off and have the hard welded..about $550 plus about $250ish for the camshaft. Before you consider going into the motor ask lots of question....also visit Dynoman Performance, A.P.E. and Cycle X which are the go to places for the 750 motor. I have experience with the motors so ask away!