Drive Train Upgrade Suggestions

Easy way to do it: get the slant six running reliably while you sort out minor stuff to get it streetable and look around for a stock or modified running 318 & 904. If it’s stock, Breathe on it a bit (cam, intake, 4 bbl carb, headers, duals) and enjoy for a while until you get bored with the power levels. A mildly modded 318 is plenty for an A body, and doesn’t require more than the lightweight 904 and 7 1/4 rear, so you don’t have to do a ton of chassis, suspension, drivetrain and rear end work just to drive it.
JMO