Blueprinting is taking all the spec's to the prefered tolerance.
This would include as an example but not be limited to:
All bearing clearances the same and set for the prefered oil.
The decks flat and square with the crank and same height.
All combustion chamber and piston volumes the same for CR.
Rods, pistons, and crank checked for length dimensions and balanced.
Rockerarm on valvestem geometry verified.
Block cam and crank bearing bores alignment verified.
All this work increases the labour needed to rebuild an engine to an insane degree. Most of it is just checking and verifying but if things are out you have to be able to do something about it.
Many general rebuild shops are not able to hold the tolerances to do this work and those that can will charge heavily for it. An example would be planing the heads to square them and balance the chamber volumes to the desired depth. Most shops plane heads with a large grinder much like a belt sander. It takes off around 0.010" where ever the operator pushes hardest. The prefered method for a blueprint would be a milling cutter or a surface grinder that could precisely remove from 0.002" to 0.100" from whatever corner you wished, and leave a perfect surface finish.
Steve Best