Think he Cut off the pipe and slid a 1" nipple over the flange and welded it fast then threaded 1" pipe elbow onto that.It's pretty simple and very clean looking.
Eric, I just blew that photo up you sent me. He built a complete new exhaust manifold system. That would make more sense as he has the original to put back in case of a re-power down the road. Going to look into that closer as my machinist could make the flange and weld the 1" pipe to it. I have pipe threaders and could do the rest OK. Will see how the hood fits later today - I hope. Choke hook up come first.