Re: rebuild on original 350
I had the same thought about decking...don't lose those numbers! I'd document the heck out of it before you pull it and drop it off at the shop too...Photos of the engine in the car, close up photos of all the numbers on the front pad, just in case something gets screwed up.
A small block is pretty simple to put together, but you may need some tools you don't have. A piston ring compressor and valve spring tools comes to mind, and I'm sure there's some others I can think of right now. You'd need a good book like the one by Dave Vizard and some consumables like Plastigage for setting up the bearings.
If the machine shop gives a warranty (and stands behind it), the price doesn't sound bad. If it were me, I would let the machine shop at least set the short block up (install crank, rods, and pistons) and install the valves in the heads The cam install isn't hard, and heads on up is pretty simple.
Sometimes though, unless you want to learn a new skill and like the "cool" factor of saying you built it yourself, it's just better to let a good shop do it. I have the skill to do my big block for the 69, and have most of the tools and can borrow the rest, but I got a good deal at a reputable shop and was happy to pay the labor and not have to deal with it.
Depends on priorities, I guess...
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!