Does this cartridge exist?

A 7 x 61 S&H super simply necked up to .308?

I know the 8 mm Kvale that is a 7 x 61 necked up to 8 mm with the rim turned to 30/06 head dimensions , but no .308" versions of this basic case

While I have never heard of it. The idea doesn't surprise me. The 7x61 has been around since 1953. The 308Norma, 300Wmag, 30-338 all came to being in the early 60s late 50s. So if someone what a short magnum 30cal in the 50s it would make sense to neck up the 7x61. Up until the 60s the 30H&H was pretty much it as far as a magnum 30.

There were many short magnums in 30 cal in the late 50s. Too many to list but most were similar to Ackley's short magnums. They used 300 H&H cases shortened to approx 30-06 length,most had minimum body taper and sharp shoulders. The short mag cases was pretty much standardized when Win introduced their 264,338 & 458 cartridges.