Yes, it does seem a bit odd how they did the V8 stuff, doesn't seem too cost effective though it appears the 260 is nothing more than a bored out 241? Maybe it was a marketing gimmick? The HP wars were just starting up and though Plymouth was the low cost Mopar line it still needed to compete with other low cost alternatives.

Remember the SBC first came out in 55, the 265 and it's equivalent to the Plymouth 260 made a touch less HP, 162 vs 167. Those early SBC had their durability issues.

I am into the flatheads. my 230 I am building is setup for 9:1 compression. I expect it to make 150 hp, 53 more than the stock 218 that is in my 51, well when it was new, lol.