If its a rod bearing it will rattle from start up. You sure thats your problem? Sounds more like an exhaust leak to me.
But assuming its your rod bearing, pull it. You could half ass it and pull the K-member and pan. Then pull the cap on the rod, if you knew which one it was, and put a new one in. THe motor is probably going to chew that one up in short order because the journels are probably grooved and need refinishing. Have fun trying to talk your engine biulder into making that happen. When its all said and done, you'll have 5 times the time into screwing with it and it wont be fixed right. Just pull it, or fix the exhaust leak. lol