I've known of people simply draining and reservicing engines that have sat for decades with no ill after affects ..... but I certainly do not recommend that practice!
Some will tell you that the engine must be disassembled and minutely inspected, regardless! That will obviously give you the best piece of mind, but a lot of money has been wasted by many people who found nothing wrong with their engines after complete disassembly.
I take a more middle of the road approach, which I think makes more sense, too!
Assuming you are satisfied with the logs and sign-off, the question is how well was the "fresh" engine protected by the assembly oil. The rod and main bearings can remain wet for decades from capillary action, depending on the oil used, but do not disturb the crankshaft, just yet! Drain and discard the assembly oil, and remove the remainder of the accessories, the oil sump, and valve covers! Do a good visual and internal borescope inspection of the crankcase, geartrain, and cylinders looking for any sign of corrosion. Good decisions will depend on your judgement. Very spotty (quarter sized or so) surface corrosion (powder) on the external crankshaft throws, or similar thin spotty corrosion on other visible iron components are acceptable on non load bearing surfaces (most active engines have some of this anyway). Iron oxide "fuzz" coating any one component, gear teeth, or load bearing surfaces is not acceptable without further removal measures and closer inspection. Any but the lightest rust on the apex or ramps of the cam lobes may be cause for engine disassembly. Don't forget the face of the lifters. If you can rub the thin iron oxide powder off with a dry rag and find nothing more than slightly discolored metal, it's likely still good! If nothing other than spotty minor surface rust (powder) is found inside the crankcase, wash or spray all oil-wetted components with mineral oil and let it drain. Remove, inspect, oil, and reinstall the safety relief valve. The "short block" is done.
No doubt there will at least be some minor surface corrosion on the steel cylinder walls. This is a judgement call as above. Quarter sized obvious surface rust spots can generally be ignored, and will disappear soon after starting. These can form within a few days even on "active" engines. Remove any that you can reach, spray the cylinders with mineral oil, and let them drain. Larger areas of corrosion, or that may hide pitting, will have to be examined more closely, with the cylinders removed. Pre-oil the engine oil passages under pressure with mineral oil before turning the crankshaft for cylinder removal. I have had very good success cleaning and rehoning otherwise good cylinders displaying considerable amounts of surface rust. Wipe away as much rust as possible with a dry rag, and if no pitting is revealed, re-hone them just enough to knock off the remaining rust and reestablish a cross-hatch pattern. A little etching (not pitting) left from the rust does not hurt anything, and will wear away in a few hours of operation. Re-measure the bore and piston for proper clearances before reassembly. I've reused the same (new) rings without removing them from the pistons, with no problems, but if in doubt or they appear stuck, remove or replace them now! Replace any disturbed gaskets and seals, which cost nothing by comparison to replace. Oil and reinstall the cylinders and finish final assembly and installation. Again pre-oil the engine and fill the sump with mineral oil before attempting a start. With a properly pre-oiled engine, oil pressure should respond almost immediately. Do not exceed idle if idle can be maintained, then shutdown and drain and refill the sump again once the oil has had time to warm. Inspect the drained oil for any sign of metal or other contamination. You're ready for the initial break-in and adjustment runs.
I actually do have some before and after shots of cylinders I've cleaned up and placed back into service. My return to service experience ranges from A-65's to R-2800's, with no failures. If anyone knows of something I've forgotten, or have a better method, please jump in and let us know. I'm still learning, too!
