Hi Hotrods 1,
This is a K model top tree. That internal machining, I've never seen. The 4 ears are a giveaway, they are used to fit the 2 electrical switches underneath the tinware.
I had a 1953 KK with that geometry, it lasted until mid-54 when they went for more trail, but its tubes were tapered like later Sporties.
...We learn everyday, I can only suppose this is a early 1952 K one... The K parts books only list one sort of tube, the tapered one, 45953-52 and one sort of top tree, 45738-52...
By the way, that earlier geometry was kept going on the flat track racers, KRs, XLRs until the advent of the Iron XR and its new frame in 1970.