Try this for a test of carb size, hook up a vacuum guage to the intake and using a length of hose, put the guage somewhere that you can see it safely while driving.For a 235, pick an RPM range of maybe 2000 to 4000 max for this test.Cruise along in an second gear, 2000 rpm, push the accelerator to the boards.At first the guage will drop to zero,then it may rise as the engine picks up RPM. As the engine nears 4000 rpm, if the vacuum reading is 3 inches or higher,the engine can use more carburation.Moderately modified 235/261's need only 300- 400 cfm, so you are close.
