The Merlin III Block will probably be fine for you. It is heavy and beefy.
I suggest to check or get someone to check the main bores for size and alignment, Hone the cylinder walls the minimum amount to take out most of the marks. You won't need to take them all out. I know it sounds uts bt trust me on this one. If you buy custom pistons you can buy for any bore you want. My piston that I have made by BRC is always on the oney and I usually have it all bored and honed even before the pistons are here, because I know what size they will measure. I can do any size or any piston you want when doing custom pistons. I do the design different depending on the application and the engine.
We always do our best to use what the customer has already if at all possible.
Ed