On the Slant 6 or any engine for that matter, other things to consider for usage, besides just HP. Their's HP potential, and at what cost Slat 6s and flathead 6s making big power in relative terms is not a cheap endeavor so be it. But on a Slant 6 engine, little things, easy to get parts , full flow spin on oil filters, OHV design, 6 intake ports as opposed to 3 siamesed types on the L heads. Also a Slant 6 can bolt right up to a A904 or an A833 trans, for those who might require an auto trans, L heads it can be done but it aint cheap or easy.. I am sticking with a 265 Flathead build for the 55 Fargo though...
I bought a 64 Plymouth Valiant with the 194 engine & it was a Great Commuter Car & when the Engine would Die I put a 225 in it the only Different was the Exhaust Pipe was Diff. that being said I used to Tow a Race car! with it for 6 years all over the East Coast! you could Not Beat the 225 engine