Brandon
A stock 1600 should easily rev past 5000 in a snap and a well sorted near standard one with a sinble downdraft weber will easily go past 7000 rpm.
I assume you have a downdraft weber and manifold fitted off a ghia, if not get one ($150 all up off ebay is the going rate), basically these are a very similar set up to a 1600 GT Cortina.
Without making major odds to the motor there are a couple of things you can do:
1: Check the carb is actually getting full throttle when your foot is flat to the floor. Not as silly as it sounds, bent linkages, stretched cables etc, pretty easy to lose the last bit of throttle movement.
2: Have a good look at your timing, no engine is going to be revvy if the static timing is still set around 4 to 6 degrees. If you slowly advance the dissy you will hear the idle come up, try say 12 degrees initially, have agood look at the bottom pulley and the manual, make sure you are timming off the correct marks.
You will be surprised in the difference in how snappy the motor will be off idle and through the revs just by doing this. Just make sure it doesn't ping when you get the revs up.
If you want a better explanation of basic timing, caruburation etc get the David Hamill book on Pinto's. (About $35 from Pitstop Books in WA, you will have it next day if you order over the phone). I know you are talking about a 1600 here but the principals are the same and that book has a LOT of good info about basis of sorting out a Pinto which by the sound of it you are heading towards.
Cheers
Shaun B