i beleive you add .6 to your piston compression with the hr+3mm crank.
for example i ran a 98mm 14.25:1 venom piston w/hr+3 and had 14.85:1 compression.
major butt kicking stump puller-IMO
used 5 gal pump pemium 93 octane and 1 quart kemco tetrathyl lead mix (affordable and safe). made 105 leaded. ran great. piston shows no sign of predetonation after 15 hrs.