There was a drag racing air cooled VW Bug retrofitted with subaru 4 valve
2.2 SOHC heads.
There's a picture of it online somewhere. 
Understand that it was unbeatable in its class. 
No air cooled OHC heads come to mind that I can think of that would be a
natural candidate. 
The soobie is attractive for the 4 valve heads, and for coming from a boxer
4 cylinder engine in the first place.  
Right now I can't even think of any "OHC air cooled car engines"  other than
an NSU rear engine, OHC air cooled inline four, mounted sideways, in the
rear.   A late 70's era car. I did a head job on one once. 
( hmmm.....porsche racing engines, from the 60's. - those are 4 cylinder,
OHC air cooled car engines )
Given the modern technology and abundance of the 2.2 subaru, and 4 vales
per, it looks like a natural. 
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Andrew Grebneff
Sent: Wednesday, September 19, 2007 8:53 PM
To: vanagon@GERRY.VANAGON.COM
Subject: OHC heads on VW luftboxer?

Has anyone ever tried ftting belt-driven SOHC or DOHC heads
(watercooled or aircooled) to any aircooled VW engine?

All that would need to match is the bore-spacings; the rest would be
amatter of making it fit.

I know BMW experimanted with DOHC heads for its twinboxers, but it
wasn't workable because of resulting lack of cornering clearance.