I had Carhex do mine a few years ago. Converted my box and sent it back in 6 days .... although i did glass bead mine before i sent it to him and requested the he not paint it. Back then he was charging $180. Get his phone number off of this link and call him to see what he is charging these days. I initally found him though ebay, but his listing right now is showing $599 due to a lack of cores. I will say it works well, 3 turns LTL, no leaks, and i got my original box back.
https://www.facebook.com/carhex1/