I strongly recommend OEM water-to-oil coolers that are made for your engine, if there were any (like volvos and Nissans). They usually mount onto the oil filter housing. You feed them with hoses that normally go into the heater core. That way you don't oil down the track once you get a rock in your oil cooler.
In general, non-stock oil coolers mounted with cheap aftermarket sandwich plate adapters tend to have a reasonably high chance of making more problems than they'd be solving. As in, if you're going that route, make sure to do everything right or you'll be blowing a motor 3 laps in because of some mystery feature that fed you an air bubble, or let out all the oil, or kept your oil at 20f temperature at a Gingerman race.
G-bodies (Bonneville, LeSabre, etc) had a battery under the seat. That said, try using a soft new auto parts store 4ga or 2ga cable from starter to the kill switch, and a low strand count (~3-10) hard-ish 6ga or even 8ga cable from a hardware store, from the kill switch to the battery. That cable doesn't need to flex, so you can go down a size, use thinner hard insulation, and still get the same conductivity. It's lighter, cheaper, and once properly attached it's less likely to give you problems.
K Car Stalker