My Dad has them working on a 550 spyder replica with a 2.4 911 engine in it. I've seen the 904 molds at his shop, I believe it's built around a Porsche 6 not VW 4 like most replicas, it will be a really nice car (I think Thunder Ranch makes Becks bodies, but I'm not 100% sure). Tom builds some really cool cars. You should go down to El CAjon and check out his shop, you'll be impressed.
There are a couple of pics of the spyder in this thread:
Best 550 Spyder colors (other than silver)