Is a 1991 360 balanced like an la no matter what

'91-'92 were the changeover years from roller LAs to Magnums. Magnums were probably being cast in '91. To be sure if the block is a Magnum, look on the sides of the block to see if it has the truck mounting bosses. If it does, it's a Magnum. LAs never had those style bosses. From the factory, roller LAs were balanced just like their standard LA counterparts. But since it's a refurb, (especially if it's got a mix of LA block and Mag heads and who knows what else), all bets are off as far as balance. I would contact Jeg's / the rebuilder and find out exactly what you have before moving forward.