The belt tensioners have a short adjustment range, likely about 1.5", thus a 3/4" long or short belt(from perfect) would be almost rubbing the tensioner on either stop. Any pulley changes will require a belt change of more than 3/4".
The 302 Explorer balancer has the pulley molded into it, not bolted on. It is not replaceable. Look above seven posts at the stock balancer on the right. Below is a custom balancer which I just received. It has the crank trigger on it, and should accept any 94/95 Mustang pulley. I needed this as a 28oz. balancer for my 332 I'm planning for. You could do the same thing with a 50oz. stock weight balancer, and there are under drive crank pulleys for 94/95 Mustangs.
Look at the stock diameter of the crank pulley, I believe that it's about 5.75" in size. You will not gain much in power or economy by going much smaller. Feel free to try it, but the cost is not cheap. I paid over $300 for this balancer, and it does not include a pulley. Good luck,