First off, I assume when you say “Monza” you mean the front engine car and not the Corvair Monza . . .
If I were building a CC (and I am not) I would sell the Monza to someone that wants to run in the Classic Category (Pro, Gas Coupe, or Altered). Then I would look at what is out there and has set records. Just looking at the Bonneville CC record holders you can see a variety of bodies.
Keith Turk’s is an 80 Camaro running a pretty near stock shaped front end. The Trackmaster car on the other hand is a stretched early Fiat Topolino. If I am not mistaken the records set in CC by Wooden were mostly (if not all) done with a chopped and stretched Crosley sedan. The Burkland B-210 is mentioned above. The Stringfellow car is a stretched Chevy Cavaliar. The Bryant car (which crashed last year) was a chopped and stretched 34 Ford coupe. The Ace Allen car (also run in the E class by Joe Timney) was a stretched and chopped Chevette (gone now after a heavy crash). Huffman runs a Studebaker. Of course there is the Blowfish. In the smaller displacement classes you see the Hondata which is an Acura RSX (or maybe a Honda Civic?). Also the Geo Metro cars run by the Hudson boys are all small but there probably isn't any data on that body over 140mph or so.
If you are looking for small you also might try to get one of the following . . .
Fiat 600 (not sure if the Fiat 500 would be considered a 4 passenger car)
Crosley
Early Honda Civic
Honda 600s
Reliant Kitten (the 4 wheel one) from England
Toyota Starlet (or Starlight?)
American Austin Coupe
Mini Cooper (not the new one from BMW)
And there are others.
One issue with the really small cars (small frontal area) is that they tend to be hatchback shaped so I am not sure how good the aero is with the blunt butts.
Lots of choices . . . .