He doesn't know what size they are. Judging from the dimensions I'd figure they're about 5 gallons.
I told him I'd buy them anyway, there must be a way to get some standardized connections on these things. For the price, it'll be worth doing some digging, hopefully the LHBS will be nice enough to help out!
I'll let you know how it turns out in case someone else stumbles onto these types of kegs in the future