Hello, I removed the leaking black tank from our '67 Safari '22. I fabricated a bracket to hold a black and gray tank. I bought the tanks from Vintage TS. The tanks are small, 8 gallons each, but we spend 99% of the time in full hook up campgrounds. Now that we are self contained, we can use the water on the road and non full hookup spots.
As to placing the drains on the bottom of the tank, is there enough room in the chassis to have the plumbing below the tanks? I'm not familiar with your frame, however, ours is approx 8" deep. This is what limited us to the small tanks.