yep thats reasonable for a stock A12...

Although a stock A14 can rev alot harder (7,000rpm) heh Teretonga!!! Ah those were the days!

Anyway back to the question:-

There will be 3 bolt on things that will give you revs on an stock A series...
A set of extractors (or even a GX manifold) with a 2 1/2 inch system
A downdraught 32/36 Weber carb
Electronic Ign.
You get these 3 things and would wont believe its the same engine.
Then you can rev the guts out of it day and night, and if she ever broke you just buy another one for $20 and bolt all the gear back on again.