Eric,
I am not sure that a fully understand your question with regards to standard HRD, but here goes.
OHV JAP engines were fitted to Diamond frame Vincent HRDs in 350 and 500cc sizes, plus there were twin, or single port models in the case of the 500. These models were made from 1932 to 1935.
JAP engines were also fitted in the earlier 1927 to 1932 models. Some were SV and the majority OHV. The engine sizes included 250, 350, 500 and 600.
Simon Dinsdale will have the data on this.
By the way I own 1931 Python Sports Triangulated frame model.
Cheers
David