Some of what you do will depend on what you are going to do with the engine. If you are going to replace or refurb/ grind the crank, some of this doesn't matter.

Look the block over for special markings. They should be well documented on the web, one of them is a "maltese cross" which denotes undersize components. I've got a 340 block with JUST ONE lifter hole oversize, meaning if I ever use it, I'll have to round up one special lifter.

Mark the main and rod caps so they go back on the positions they came off of

If you intend to EVER reuse the cam, mark the lifter locations, IE drill a 2 x 4 or something so you can put them in order.

If the engine has a large wear ridge at the top of the cylinders, you may need to ream it before removing the pistons, otherwise you can break a piston/ ring. On the other hand, if the ridge is that large, you won't be re-using the pistons, anyhow.

Be sure to watch for undersize rod/ main bearins if you are not going to have the crank ground. That means marking the pistons as per hole, and the bearing shells as per position, at least until you get things sorted out.

Be sure not to get the block "oil-less" and then leave it sit around to rust.

If you are going to have the block "hot tanked" you need to plan on replacing the cam bearings and distributor bushing, so if that is what you will have done, look for and pull ALL the oil gallery plugs, as well as the "freeze plugs." Some inatentive engine shops will hot tank a block with the plugs in place, and "one" of you might not notice.

(I once instructed a shop, working on my heads, to "hot tank them and replace the plugs." When I got them back, everything looked OK, they were painted. I put them on, and a month later, the plug on the rear of the head leaked--rusted through. They had painted over the old plugs--so PULL THEM OUT)