318 won't rev past 3000 rpm

I am guessing that you have run it long enough to blow out any debris in the exhaust, plus I assume it is dual exhaust and you would have noticed more exhaust on one side than the other (assuming only one side is restricted).

My 2 choices are

#1 - seized advance weights in the distributor - I have seen this before, pull off the cap and make sure you can twist the rotor to advance it, it should spring back when released

#2 - the factory sock on the fuel pick up (kind of like a filter) in the fuel tank is plugged / gummed up with varnish from the time sitting seriously restricting fuel flow.

Also, I hope that you do not have one of those silly 3" diameter air cleaners, or cheap foam and chrome edelbrock ones, try running it without the aircleaner.

Good luck!