It's a TM made to look like an RH..
Are you sure John? it looks like the real deal to me. RN370/400 with long stroke top end. Notice the spacer under the barrel and the narrow tube used in the rear subframe.
Doc the cylinder head is totally different to an RN, it looks like TM and the bottom of the fork legs are different, they look like machined down TM forks and what's with the barrel spacer? The lower fork legs are also longer than RN fork legs. The flat seam around the edge of the tank is different to RH/RN also.
It looks to me like a very good copy of an RN possibly using RM370 wheels, triples etc and a hand made tank, not sure if it's an RN frame or a copy.
Have a look at the pics of Dave Tanners RN400 on vintageworksbikes.com for comparison.
