How much cylinder bore ridge at the top of ring travel is there? That needs to be removed. Also, not a good idea to try and rebuild a block with too much piston to wall clearance from wear. Go by the max bore wear in the factory manual, or very close. KB lists a piston that is hypereutectic (stronger than stock, and lighter) that will fit with your stock rods and give you 8.9 to 9.3 compression depending on head volume of the 906 heads. This is your cheapest route with an overbore. The motor will love the extra full point plus compression, and the pistons show big valve reliefs for all the cam you need. Depending on how much converter stall you will have (assuming automatic here) you can go pretty big on cam if you have a high stall ( 4000 or more) . I have run a 268 at .050 and .540 lift on stock rockers with a mild lobe that lived with the stock valve gear up to 6,000 rpm. Less stall will dictate staying pretty short on duration, go by cam manufacturer recommendations. Stock converters come in low stall or high stall, obviously you want the high stall if you want to go with a stock factory converter. Remanufactured converters can be had for around $120 in high stall. High stall will be somewhere between 2200 to 2600 rpm as a guess. Low stall is listed at 1800, real low end killer.

Hear is a small stroker combo that yields 9.6 to 1 compression at 4.350 bore. 4.375 bore also available with these pistons.
Ross forged pistons, 99907 4.350 bore or
99906 4.375 bore. (max overbore for most 400s.
Chevy big block rods ,aftermarket 6.800 long
Offset grind the crank to 3.525 for a stroke increase of .150
This will produce a light rotating assembly that will make 418 cubes with 4.350 pistons, or 424 cubes at 4.375 bore
This is a cheap stroker combo for a 400 when you consider that you will need to rebuild the old rods, and buy pistons anyway, and possibly regrind the crank.