I'm at work, so I'll check back in after while. I am no longer an engine machinist, but not because I wash't good at it. I worked for the best shop in my area and was a cylinder head specialist. Life changes and more money were a necessity...so I only do some performance work on the side from time to time.
Now that my qualifications are out of the way...I would like to know more about what you plan on (spec wise) for this build. Things like cam/valve lift, RPM range and redline, what kind of shape it the bottom end in, What type of porting you plan on, rocker arm choice, etc.
On the preliminary side of things...use a soft wire brush (3" diameter) in a drill to clean up the chambers. Use a very sharp putty knife or razor blade to remove the gasket material from the machined surfaces. DO NOT USE a rotary scotchbrite or any other abrasive under the power of a drill or grinder. This will cause hills and valleys, requiring the heads to be resurfaced and intake leaks. You can use a flat block with 80 grit on the intake and exhaust mating surfaces. On the deck side, find the flattest table top, patio or floor you can and use a wide piece of 80 grit. I use a belt from a floor sander that is 8 inches wide by about 22 inches long. If you have a rental place near by, you can probably by a new one there. The best find is from a hardwood floor sanding contractor that uses Lagler/Hummel floor sanders. They will use them until they are too dull for floor sanding, but they are perfect for flat blocking the deck side of iron cylinder heads. This will also show warpage, though it won't tell you how bad.
If you plan to port the heads, don't do the dreaded "port match". There is nothing to be gained there and may even cause power loss due to "bell mouthing" the ports. It causes areas with "eddies" like a stream with calm spots. Those calm spots kill air flow in a major way. Stay away from the floor of the exhaust side, except to polish. You can polish both intake and exhaust ports because fuel atomization due to a rough intake port is an absolute myth. Those rough areas are just a place for droplets to collect and turn into carbon and sludge. The most power to be gained from those heads, as well as most others, is under the valve in the bowl area. You can also trim the guide areas leading into the roof of the ports to help direct air flow and reduce drag.
You can use iron filings with carpenter's chalk mixed in and a large magnet to check for cracks. The magnet's power will decide the results. If you have some MDF and a piece of rubber around 1/8" thick, that is big enough to cover the deck side, you fashion a make shift pressure tester. Use a 4" hole saw and cut 4 cylinder holes, then drill the head bolt holes. A head gasket will give you the locations for said holes. Get the appropriate fender washers and nuts to bolt the plate to the deck side. Of course you'll need the rubber as an air gasket and it will need the same holes in matching locations as the MDF. Now you have 2 holes to seal up on the intake side. Just use some of your scrap rubber and MDF to make a couple block off plates that can be attached with a C-clamp. One of those plates shoot be drilled and tapped for 1/4" NPT threads...this will allow it to accept a male air chuck. Once you have it all together, you can hook your air compressor up to the chuck (DON'T GO OVER 30psi). 20 pounds should show a crack in a hurry. The best way to find a leak is the same way we do for tires...dish soap and water in a spray bottle. You need the 4" holes where the cylinders are to check the chambers.
