I took the instrument cluster out of the car to change the tach (the clock didn't work) I put everything back and now the car won't start. It cranks fine, I get voltage to the distributor. I have to check for spark today. I am wondering if there is anything else (say through the tach.) necessary for the engine to run besides the voltage to the dist. and fuel? Does the tach. somehow play a role? thanks for your help.

If you are getting power to the coil then it should start, unless you are out of gas (I've done that plenty of times and felt like a dumbass lol). Did you check if you are getting spark yet?