I believe your 240 has the distributer on the side of the engine vs the rear end of the cam like most of the 740's, in which case the I-shaft timing is critical. Since you know the crank/cam relationship is correct, you could look at the position of cylinder #1 cam lobes to decipher true TDC (vs the top of the exhaust stroke), then pop open the distributer cap to see if you are even "close" to firing #1. You could MAYBE then loosen the belt and try to get everything "somewhere close" to being back in time, but you would then have to put a timing light on it and crank it over to see how far off you were, then loosen the belt again and re-adjust, etc...... A VERY tedious task.

Get the pulley off.