you need to avoid a V5 that says saloon with provisos. Buggies got registered as all sorts in the days of local registration offices some got beetle convertible not ideal as you could buy a standard VW version, sports, special, home built kit, 4x4 or any buggy make are common but many got built and not registered as such so still show the original log book description.
the proviso is we have a V5 that shows make, invader beach buggy, year of reg 1971 but showing saloon body type, the last swb I rebuilt and sold had beetle 1200 but convertible under type, base car was 1964 reg and vin but on a 1969 registration date and plate.
The rules since 1998 state any new swb build or modified lwb floor pan buggy you had to go through iva test now sva test.