Not sure this is going to work as i'd planned. I stripped out an HZ lump and had a butchers.
Compared the PY piston and rod to the HZ piston and rod. The rods seem to measure the same circa 122mm c-c. However the HZ piston is about 10mm taller from centre of gudgeon pin to face of piston than the PY piston.
Which if I did what i'd planned; PY rods and pistons on an HZ crank, then i'd end up with very little compression.
So I may have to use the PY rods on HZ pistons giving me 9.5:1 compression ratio
I may have my AAV engine apart and see what the pistons look like in that.
Need to get my hands on a dial gauge.