What tool are you guys using to help find the center of the main bore so you can check the block deck height? Did anyone make one on their own?

For block height..If you are good at measuring you can use a mic and a small pin inside the main bore, then do the math. Take your time and make sure its seated properly. It's probably not how a "shop" would do it, but if its done right, well, it will be right. No fancy fixtures.

I get the math. (Measurement + 1/2 the main bore dimension = deck height). But I don’t understand what you mean by a “small pin.” Also, are 10-11 in. Micrometers available? Or are you using something else?

a piece of round steel stock cuz with the mike being flat & the bore being round the mike will not sit down flat on the rounded surface.

There is also a deck height mic available that doesn't have the full round beam like a regular mic. Don't remember who makes them, though.

pin size can be arbitrary..1/4 would work..see pic above

You could use a round pin & a tape (dont use the slotted chrome hook on the end) & several helpers which will get you "close" & purchasing that big of mike will be expensive unless you plan alot of use to get your moneys' worth. what I would suggest is putting the block belly up in the back of your pickup & driving to the machine shop & have/pay them to come out & take a measurement which would take several minutes & for sure call ahead & schedule a time (& hopefully you have a shop close by).

I used a 12" Mitutoyo caliper similar to the method of Hot 340 except no pin.

I did my last block just like this.. worked
great

Is there a reason you can't throw a crank and piston/rod assembly in a bore and check it that way? Pretty much every aftermarket set of pistons has a CD within a .001" and a set of rods made by a good company have about the same C to C distance. Throw the same piston/rod in each corner and you know if the decks are parallel while you are at it.

No special tools, and more accurate than a tape measure and straight edge.

Stock rods lengths can vary a bunch, I've seen 426 M.W. rods have .008 differences in the center to center lengths
another thing to keep in mind on stock cranks is having the rod journals exactly 90 degrees away from each other at the top and bottom of the stroke, lots of them don't
Lots of errors on most mass produced parts in our cars

I usually use a 12" caliper as well, but they are not as precise as a micrometer. When using a micrometer, you can get a .2500 ball with a rubber holder for the anvil of the micrometer. That makes it easy and accurate.

Here's a micrometer for you. Then you can do it yourself for many years.

mike

I use a 12" caliper and do the math, but I don't think it's perfectly accurate. it will get you pretty darn close.

Remember that the main bearing bore (as shown) is not the journal size, and not listed frequently.
Some bearing catalogs list the actual bearing OD, but that may not include crush.
Doing the same measurement using the actual journal in place removes this variable, instead subtract 1/2 of the measured journal OD (duh).

I have a std block and want to bore it .030 over. I'm thinking of going stroker and looking at pistons from dish to flat tops. Some are 2.05 to 2.067 compression height. I'd like to know my deck height so I can figure out which pistons will do what I want to be able to do. I'd like to start out around 10.1 compression but have the option to increase it with a thinner head gasket if/when I want to go faster. Can't stick a .030 over piston in a std bore block.

Every original stock Mopar V8 block I've taken apart and had blueprinted was way off on the stock deck heights, a lot taller than the NHRA specs. call for
I've seen them tapered from front to back also
My main message is count on having your block deck cut to get it close to stock blueprint heights

or mic the bearing bore of the block and add 1/2 of your dimention.

Every original stock Mopar V8 block I've taken apart and had blueprinted was way off on the stock deck heights, a lot taller than the NHRA specs

True, that. Almost every data point is looser than called out.