Clean, clean, clean everything. Then clean again. Everything must have no trace of brown on it.

Plastigage, like Jim said. Don't assume the machine shop got it right. Oil the lifters and their bores, and check that the lifters sink slowly through the bores from gravity alone. If they don't hone the bores as needed -- this assures the lifters will be free to rotate.

Assemble with lots of motor oil on all pressurized bearing surfaces, and in the cylinder bores. Assembly lube on all cam lobes, lifter friction surfaces, and rocker arms (I use Redline brand, FWIW). Assembly lube on the main seals, assuming you upgrade to the modern kind.

I use sealant on all gaskets except the head and manifold. Permatex Hylomar works very well -- apply thinly to all surfaces.

Initially torque the head to 61 ft/lb using anti-seize on the bolt threads.

Run in: Keep the engine running for 20-25 minutes on first start, varying between 1500 and 2500 rpm, to establish the wear pattern for cam and lifters. Do NOT let it idle -- you can tune it later. Shut down and change the oil and filter.

Let it cool down completely. Retorque head to 69 ft/lb. Readjust valves.

First 500 miles, use no more than 2/3 rpm and 2/3 throttle. Change oil and filter at least once during that period.

After 500 miles, retorque head to 69 again and readjust the valves. You can then gradually work up to higher revs and more throttle. Keep an eye on the valve adjustment for a few thousand miles after that -- if the head gasket has finally crushed fully, they should not need further adjustment for months or even years.