What STIDUB has said spot on... I have two Sparco Pro-2000's in my 70 bug, but any wider and I think you'd have problems. It's really the "wings" measuremement that's critical I've found.
I've got pics of my fitment up here somewhere... on another thread recently about exactly this subject.
Also with used seats be careful of the date (FIA spec gear expires 5 years after manufacture) and also the ADR compliance.... if you can't prove they're ADR compliant (markings or a certified test report) then they're also not legal.
VWDCQ vice pres & web dude - vwdcqinc.org.au
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My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI -
http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners