Terry is right on the rings. I used the term too loosely because in a lot of ring packages (more for modern engines), you had the choice of chrome top-rings or moly . . . we got used to just saying chrome-moly rings and then we would see what the manufacturer had. Most of the better ring packages today use some sort of moly/plasma coating - and rings can be made of cast iron, steel, etc.. There are a lot of ring choices in modern engines and quite a few if you have pistons with metric rings in a flathead.
If I'm building a custom big-bore flathead, I usually make sure I can get the rings I want first - and then have the pistons/bore done to suit. The metric rings are sized for metric bores, so they're not available in all the standard over sizes that we're used to in the USA. I'd probably check with Egge to see what is available.
If your engine is 286 cubes, then it is probably 4 1/8 stroke and 3 5/16 + .020 bore. That would be just under a 85mm ring - which is for a 3.346 bore. If it was mine, I'd probably go to a 85 mm bore (if you can get away with a very slight overbore) and get pistons made for 1.5, 1.5, 3.0 mm rings (check and see what is available in 85 mm).
I like the modern metric ring packages - much better quality rings, a lot less friction on the bore, etc..
PS: I've found that Ross Pistons is more than happy to work with you on custom piston sizes, ring packages, custom compression heights, etc.. -- they are what I usually use. If you call them directly, they can be super helpful. Then you can usually order the pistons through Summit Racing and only pay a small 'up charge' for the custom options.