Hi all what would be involved in converting a GPU to a usable aircraft
powerplant ?
looking specifically at the O-290.

Ive googled and not come up with much.

That's really an ancient question! A good bet is to contact EAA (you are a
member, of course) and get references from them -- old copies of Sport
Aviation (now available on CD-ROM), and maybe a dedicated book on the
topic.

Ed WIschmeyer
Member, EAA Homebuilt Aircraft Council