I talked to Tim about 18 months ago about building me an XP470. He said he could do the work, but also that he was contemplating retirement and could not guarantee he would be around to support the engine.The 4 big shops in California are Tim's engines of Long Beach, Victor in Palo Alto, Ly-con in Visalia and Corona Engines in Corona.
Tim's will quote slighter higher than some shops because he replaces EVERY nut and bolt and threaded stud. Most shops only replace what is required. Tim's will send you a spread of all the stuff he promises.
I'd have an engine overhauled at any of these shops.