How do you make sure the timing on the distributor is right after changing the timing chain and gear on a 1993 Chevy 350 V8?

you must know where the #1 cylinder is pull the plug then rotate crank until the piston is at the top of its stroke visually looking down the spark plug hole then pull distributor cap and see if rotor is pointing dead center to where the #1 plug wire is on the capif not pull distributor just enough to rotate rotor to that exact spot rotor will always move ahead slightly when distributor is pushed back down so adsust for this good luck

2nd answer

Proving you have installed these parts correctly, using a manual, the next step is using a timing light on the timing marks on the crank. Also, there is a connector that must be disconnected in order to obtain the correct timing. Its a 4 wire connector which basically relays the info to the computer. In this process, the computer is left out, while you make a manual adjustment. When finished adjusting the timing to the proper degrees (it being 10 or 8 etc..)reconnect this connector. The computer will then maintain proper timing from there on. Again, this is only if you used a manual and correctly did the wiork. Good luck. JP