Swing axle rear ends were standard fitment on all regular (ie non 1302/1303 or Auto) European Beetles right thru to end of production. IRS rears can handle slightly better but tend to be weaker, more complicated and heavier than swing axle. I've been building and driving swing axle equipped buggies for 40+ years now with no issues.
It's easy enough to get a long wheelbase chassis correctly registered as long as it's completely original in spec including floorplans. Short wheelbase builds need to pass an IVA test to be legal though.
There are lots of good Lwb bodies available: Californian, Doon, Jas, GT, Volksrod, FF, etc.
Californian:
