I'd go for a more conventional lowrider rack. They mount in normal, supplied locations, like on my former 1990 Cannondale ST400. It also won't weigh a million pounds. Unless you're going for a rack with a platform like a conventional rear rack. I'd check Velo Orange for stuff, not just Riv. Or a used parts bike store/co-op/non-profit, of which I am sure there are many in the Detroit area. No one cares about used racks, and they're often priced very cheaply. And since you're not going for a Concours build / bike, it doesn't make any sense to pay Concours prices when plenty of other very serviceable options exist.