In need of 283 .030 pistons

[Accelo]

Your pins and rings have been installed and the block bored to the pistons. So no returns. I assume you are attempting to salvage all the work you have completed.
Other pistons may not fit the block. Forged or cast pistons take wildly different piston-to-wall clearances.
I did the same thing years ago. When I read the "* fine print" It mentioned the lower compression height. In my case, it was .020 lower.
This is done so the people who deck the block are not running into piston clearance issues.

I agree "It might be cheaper to have the block decked". That typically includes the intake manifold machining but not always. Decking the block requires disassembly.

Possibly you can find heads with smaller combustion chambers. That leaves the quench quite large and not conducive to power production.
As an interesting comparison, LS motors have the piston sticking out of the bore at a nominal .005 to maximize the quench.