Your plan is a good one, not every engine needs rebuild. The cam would be my only concern, but if you say it was only stains, then thats ok. Valves are really hard and it takes a lot to hurt one, cleaning them will tell you what you need to know. Lap the seats really good, install new seals, and assemble. Engines were done this way for years. Be sure to use assembly grease on the bearings and add some heavy oil to the oil pump.
Check the ring gap on a few of the top rings. Insert the ring in the bore, then using the piston inverted, push the ring down till the second ring stops the piston. Grab your feeler gauges and check the gap of the ring and compare that to the spec's for your engine. This will tell you if the rings are worn. While at this point, check for ridge wear at the top of the bores. If the pistons came right out, the wear must be minimal, there is a danger of breaking rings if the "ledge" is to great. New rings are more likely to break when the sharp edges hits the wear ridge of the block. Ridge reamers were commonly used to cut the ledge off. Straight stone cylinder hones can do it also.
I just degreased a Pontiac block this weekend with Castrol degreaser and a power washer, its as clean as any hot tanked block I've got back. I used the red pin point tip on my power washer to get down all the oil galley's. The red tip also strips paint really well.
Joe
