You know, I love the looks of the RM370 but I have never ridden one and I have no idea how they perform. But... I have owned an HL. It was (still is I guess) a ProFab framed version with a 76 TT engine. As setup when I got it, it ran 79 RM400 forks and S+W Stroker shocks, for 11" front and just a shade under 9" rear.
I'll be honest and admit that it was never as good as I imagined it would be. The forks were harsh and never really matched the weight of the bike, and the arse end was horrible. It sent every jolt straight up my spine. It was heavy and hard to start as well!
That said, I loved the look of the thing with its cobby look and that big lump of an engine. It also handled OK, especially in a straight line over rough ground where it tracked dead straight. It was fast off the line (I guess it just got the power down OK) and I actually beat everyone to the first corner more than once, including Maico 490s and the like. That surprised the heck out of me!
I kinda miss it, but in a nostalgic sort of way. I actually far prefer riding my 75 RM125M! I have no idea how an HL goes setup with really good forks and shocks, but for me at least mine would have been far better restored to original and sitting in my loungeroom...