1963 Dodge Dart 270 Convertible for the Wife

If you want to know more about this engine, find and report the stamped figures (numbers and letters) at the top of the block, facing the sky, below the № 1 (front) spark plug, just inboard of the coil and alternator lower bracket. There might be grease to scrape away to find the stamping.

Be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example here, here, here, here, and here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective. The good news is that you don't need to go to Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.