Installing your nice fat Racemark / Raid steering wheel can be a real pain if you do not have all the necessary parts like hub, horn button and horn button ring.

Been there done that:

I use a modern Momo hub (collapsible, yes! ) with an adapter from this source:

http://shop.simoniracing.com/us/prod...ategory_id=176

No affiliation - and please disregard the decorative females.

The adapter comes with a horn button holder-ring fitting Racemark wheels but with an opening for Momo horn buttons.

Voila: now just enjoy your nice vintage steering wheel with easy to source fitting kit and Porsche horn button!