Quote:

Would taking a 400 motor, and having it bored out .010 and use a 440 .030 piston help bring up the compression?

I see you are asking about using a 400 crank and 440 pistons in a 400 block. There were several variations, by year, in 440 piston compression heights (pin to top of piston). Even some replacement pistons had variations from factory specs.

I have no idea what you have. But for example, I measured:

440 piston: 1.924" CH
400 piston: 1.826" CH

The block height can also easily vary 0.030" from the factory.
Here is an example, put in your numbers:

1.69 Stroke divided by 2 (3.38/2)
6.358 Rod length
1.926 Piston Compression height
------
9.974"

If the block was 9.980", the piston would be 0.006" down the hole.