Jake,
There is a Heritage II small head available, of course, but there is no speed switch provision for model groups D50-D80, 1CR or 1CB-3CB but rather the 516-S7 and H1-L2. The Heritage I small nozzle might have had the additional speed switch provision for models 1CB-3CB.
You can adapt an H2 belt lifter to your D50 nozzle using these parts:
144081 - Belt lifter body, black
144181 - Belt lifter spring washer (order 314890)
144281 - Belt lifter hook (order 144291)
144681 - Belt lifter flat washer
144781 - Belt lifter mounting screw
145481 - Belt lifter bearing
146384 - Belt lifter label (top)
146784 - Belt lifter label (bottom)
Additionally, if you like you can order these other parts:
140869 - Bumper end rivet
147984 - Bumper, 13"
~Ben