He moved to bass because Iggy had signed a "solo" deal with Mainman/CBS and went to London to record his next album, taking James Williamson with him. Initially there was no intention of involving Ron or Scott, or of it being a "Stooges" record. In the mid-seventies Iggy stated he'd also wanted a new band name, The Users.
After trying out various bass players and drummers in London, and not liking any, James suggested getting the Ashetons back. Which they did. Ron moved over to the vacant bass player spot, supposedly only until they could find a new bass player at which time he'd move back to guitar.
Re Jimmy Recca, I've no idea at all. Natalie, any clues?
Hope that helps