With the head off you can feel the upper half inch of cylinder wall for any ridge. The maximum amount of cylinder ware will be at the point on the cylinder where the top ring stops. The ware on the cylinder wall will somewhat diminish further down the wall until the area that the rings stop at the bottom where it increases again. To determine what that cylinder will clean up at when bored you need to measure the bore at the most worn place (just below the top ridge) and at 90 degrees to the crank or piston pin.
For example, if your bore is 3.5 in. (measured at the very top and very bottom) and just below the ridge it measures 3.520 in. It does not mean you will be able to bore it .020 over and think it will clear up. Even if that cylinder is the most worn you will have to have it bored .030 over because it is very difficult for a machinist to center the boring bar that accurately plus the fact that the cylinder tends to ware more on one side then the other and if a machinist centers his boring bar in the worn area, you will end up with a bore that is not centered over the crankshaft.
A tool called a ridge reamer can be used to hand cut the majority of the ridge away. This was meant to allow the piston with the rod to be removed. If the ridge were excessive you would not be able to get it out as the ring would hit the ridge and stop it. Sometimes a mechanic will use a ridge reamer to remove the ridge and take a cylinder hone to smooth the top of the cylinder and deglaze the rest of the cylinder and use that cylinder as is with just a new set of rings. This may work for a short time but is not an engine overhaul. This is often done when someone wants to squeeze another year or so out of an engine that has been burning oil.
Before removing the rod caps you should note weather the caps and rods are numbered or marked as to which cylinder and which way is front. If they are not clearly marked be sure to mark them. (cap & rod) If the pistons are to be reused, be sure to mark them too.
After removing the rod & piston, remove the bearing shells from the cap and rod and look at the back side for the size marking. If it is an oversize (actually an undersize) it will have a mark like, .010, .020, .030 or such. If it is standard it may or may not be marked. If marked it will be (std.) Look closely for any shinny spots on the back side of the bearing shell, which would indicate that the shell was moving in the rod. Shinny spots will probably mean you will need to have a machine shop resize the rods. Look at the bearing surface, it should look smooth and have a flat gray color with no copper showing. Some high performance race engines may use a all copper bearing shell but you would not normally find that in a street engine.
Reading bearing ware is an art in itself. Piston ware is even more so. By looking at the ware patterns of a piston and bearing shells, you can see the history of that engine. At a later date I plan to write a tech section on the reading of ware patterns. For now you will need to rely on your machine shop as to what needs to be done.
Some oil pumps can be rebuilt. Your manual will usually cover that. On many domestic engines it is better to just put a new one in. The same goes for the pick-up tube and screen. If the block is to bored and maybe main bearing alignment checked by a machine shop, make sure you ask that the block be cleaned and the oil galleys cleaned. If the block is not sent to a machine shop and you just deglaze the cylinders and rering it, you still must clean the oil galleys by removing the galley plugs. Many British cars have screw out plugs but many domestic engines use a "freeze plug" (as they are called).
It is a good idea if you don't have the facilities to clean parts, just have the machine shop "Vat" all of the parts. You can clean all the nuts and bolts in any small container. Don't get them all mixed up together. Oil use to come in quart tin cans and they made good containers for the nuts and bolts off different sections of the engine and by adding a cleaning fluid in the can and just let them soak. Now, oil comes in a plastic container. You can still use them by cutting off the top half and putting your nuts and bolts from each part of the engine in them and adding a cleaning fluid. Mineral Sprits, Kerosene, or Diesel fuel work well. Be sure they are placed somewhere they can not be knocked over or cause a fire.
Now is a good time to clean the engine compartment and look for things that need to be corrected. Like frayed wires or broken motor mounts.