Maximum dia. on 45 fin drums, ('58-'65), is 12.100"...you will need at least .10" for a clean up cut, and maybe more if the linings are pitted...so if they're close to max., and "haven't" been turned yet, there isn't any service life left in them...
...also, Buick aluminum drums are NOTORIOUS for badly oxidizing between the iron lining and aluminum drum, (dis-similar matals)...if your's has that tell-tale white oxidation powder between the lining and drum, they're pretty much junk...there's no way to get rid of it, and it will continue to oxidize, which in turn, pushes the lining away from the drum, causing cracks in the lining, and when you have them turned, you end up with a dangerously thin weak spot in the lining...
I see alot of them advertized as, "alot of meat left"...well, there's no way of telling that until you measure them with a set of caliper's...you can't tell by just looking at them...
Hopefully, this helps....I've got alot of experience with Buick finned aluminum drums, and would hate to see you pay $100, $150, $200, for a pair, do the machine work, install your hubs, and then have them be junk...