I am hesitant to take anything to a machine shop unless I know I need machine work done. Once they have your engine, they are going to want to do it all and buy parts from the cheapest source they can find and mark them up. Taking a head in isn't a bad idea if you don't have machine tools. I worked a lot of heads in the 50's, 60's and into the 70's. Checking the surface on a head is nothing more than laying a straight edge across it. To check for cracks, I plugged the water outlets and laid a head on a table, chamber up. I filled the water jacket with Diesel and let it set a day or so. If the head is cracked, Diesel will find its way into the combustion chamber.

My thing is really GMC and Y-Block Ford, but Chev isn't that much different. I used to buy NOS valves on eBay until quite a few years ago, I realized I had a couple of hundred valves and will never use them. I still see lots of valves on eBay.

To check valves guides, buy yourself a cheap small hole gauge.
http://www.starrett.com/metrology/m...amp;displayMode=grid&sortBy=none/asc They can be bought much cheaper on eBay. And then a mike. Modern machine shops tend to try get stem clearances too close and then they seize when they got hot. If your guides are within spec, leave them alone. If they are bell mouthed, they need to be replaced or knurled. Knurling and then reaming to spec used to last 50,000 miles with the sorry oil we had. If you have your seats ground, make sure they don't get them too wide. I see a lot of seats way too wide and then valves burn in no time.

Not all blocks need to be bored. Lay a ring on top of a piston and measure the gap at various points. If the taper is within specs, hone it and install a set of cast iron rings. If the taper is not within spec, then consider a hone job.

Cam and lifters wear in together. Don't mix them up. The push rods don't care where they are at. If the cam hasn't flaked or galled in all these years, it will still go a long time.

I guess my main point is that I have seen big bucks go into rebuilds by machine shops and they wind up in failure because they just don't give these old engines enough clearances.

50 years ago, we only replaced what needed replacing because we had no money. And we ran all the clearances at the wide end of the tolerance. And we had practically no catastrophic failures.