Need advice with new heads

Bad idea! Pull that bronze gear out now before you get the motor going! The bronze gear breaks down quick and leave filings in your motor which will tear up your bearings. If your motor is a magnum block it should have a cast iron gear on it but I'd pull the cam to make sure. If it does just use a hardened intermediate shaft and you'll be just fine (got mine from summit for ~39 bucks). If the doesn't have a cast iron gear get a different one. That bronze gear you got is designed for racing because those guys are always in that motor changing and cleaning the inside (think nhra top fuel dragsters). Has far had the roller rockers go I use comp pro mag series but yours is a mag block and should have mag heads. If they are mag heads you could get that out of a junkyard from a newer motor. If you go this route I'd take the arms to a machine shop and have them checked out first before I used them