Seen this question asked on many occasions, here's the HG's for dummies version
1) Stock HG = 1.37mm compressed
2) Stock head = 116mm deck to valve cover surface
3) Stock block = 198.5mm from deck to main bearing saddle
If 2 and 3 are less that amount needs to be added to 1 to retain the stock compression ratio and squish/quench.
When resurfacing the Block be sure to take the Timing Case along to have it done at the same time or your new HG will fail in miles.
Block measurement = 198.5mm/7.81"