If you've got a spare 2 US grand you have another option which will yield over 223 cubic inches.
First, you'll need to start with a 200ci block.
2) Next use the Aussie or Argentine 221 crank, which has a 3.46" stroke.
3) Then cut the crank pins down to 1.931".
4) After that, fit six Datsun 280 ZX rods.
5) Then use US Zolliner 3.70" pistons, from Fords latest 5 liter Quad Cam V8.
6) The pistons come up about 200 thou above the block, so you'll need to use a thick copper gasket. The rings will fall about 25 to 40 thou short of the top of the block.
7) Next, purchase an ARP stud kit to bolt the head down to the block.
8) Finally, you'll need to dig up a set of aftermarket 2.3 HSC pushrods.
All in all, its pretty easy.
Piece of cake.
The conrod to to cam clearance was improved on later cams after the 250 came out in 1969, so as long as you use the aftermarket camshafts or a post 1969 cam, you have 53 more cubes.
Remember, the 200 is the smallest and lightest all iron I6 in the world for its capacity, and its pretty easy to get another 23 to 28 cubes using available parts if you are prepared to rebuild an engine.
The Ford I6 is narrower, shorter and shallower and tougher than any other I6 engine its size. As a pleasure boat engine, its hard to beat!