RE: HB engines??
Dan,
The Blitz differed externally from the standard HB.61PDP, by having a black cylinder-head and the PDP lettering on the left-side engine bearer was black, rather than red...
The Blitz clearly had PDP. The question is if it had something other than cross-scavenging and a baffled piston.
I don't think it did; just more exhaust timing and a longer blow-down period, to better exploit a tuned-pipe's power boost.
EDIT: Improvement.