1) OE head thickness spec is 84mm/3.31"
2) Standard head flatness spec = <0.05mm (.0019"), limit 0.2mm (.008"). If they're bowed more than .004", I'd consider replacement heads.
3) Limit total removed from deck + heads to -0.2mm (-.008").
4) Check valve guides for looseness - particularly exhaust guides - replace as necessary with modified guides w/ring clips.
5) Clean exhaust manifolds and belt sand flanges to flat surface.
6) Remove freeze plugs and block drains, scrape/clean water jacket scale/sediment, replace freeze plugs.
7) Use bottoming tap to clean deck threads, afterward measuring clamping range of bolts/washers/heads combo - or use head studs to avoid later head sealing issues.
8) Apply anti-seize on crankshaft sprocket and balancer surface.
9) Apply RTV smear under outermost cam block parting lines to prevent oil leaks.
10) Apply RTV in F/R cam tower corners to prevent oil seepage from valve cover gaskets.
11) Apply 2 coats of Copper Spray-A-Gasket sealant to both sides of lower intake gaskets and to the head and lower intake flanges.
12) Clean the upper intake passages and EGR passages (if you have EGR).
13) 182Nm +/- 4Nm (134 +/- 3 lb-ft) torque on crankshaft bolt (new spec)
14) 110Nm (80 lb-ft) torque head bolts (new spec)
15) Felpro oil pan gasket (there are 2 - use the better one and add RTV in the corners per instructions)

There's plenty more, but any good machine shop should know most of the clearances and how to put it together. If you tell them too much, you might scare 'em away. <img src="/forums/images/graemlins/wink.gif" alt="" />

Frank