I am trying to identify what engine will fit in a modified slimline frame (the numbers show it to be from a 1961 99.). The best clue I have is that I acquired this frame from a classic triton (500cc) guy who raced. I have lost touch with the guy and I am now looking to pass it on.
The frame has been modified in the style of a ‘lowboy’ (see picture). This reduces the height of the frame by about 1 and a half inches to 19 and one eighth inches. More curiously, the lower left frame rail has a large welded indentation presumably to accommodate a crankcase/primary chain case (see picture). The engine mount dimensions look smilar to a standard Norton. There is 3 inches between the front engine mounts.
I have visited Unity Equipe who specialise in featherbed framed specials and John wasn’t sure what was intended. He thought perhaps a big single but was stumped by the cut-out which was on the “wrong side”.Jackie at Unity suggested I try this forum.

Hence, I am looking for information, advice, contacts on ‘lowboys’ and more especially why the frame has been modified in this way. Can anyone help?

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