Some are freaked out about using them mixed and some aren't. Personally I think I would use as is as long as the rubbing surfaces are all good on the rocker and the pivot. I have some big 'O' and little 'O' rockers. Does anyone have any little 'O' to trade for big 'O' rockers?
They should be kept together, for the same reason as when you pull a cam/lifters/pushrods - I remember reading this in the overhaul manual (many) years ago, that stated the wear-in or hone pattern that develops between the contact surfaces are unique to those parts, and that the parts have to go through the same process if they are mismatched on reassembly, which could cause accelerated wear/premature part failure. I believe that to be on the high side of extremely remote - if you use assembly lube, and lubricate everything like it should be, they'll probably be fine. I still keep mine together, marked or cataloged.
I don't consider myself as a professional engine builder, but I built my first one ('57 PowerPac 283, 30-30 solid GM cam, 327-300 heads, 11:1 TRW pistons, original stamped rockers, 43 years ago; multiple small blocks and big blocks (even a couple of FoMoCo's) since. I have never had a reused stock rocker fail, but I have checked them all for problems before reinstalling them. Last I heard, the original 283 was still at it. It's just a matter of personal preference - I know roller tips are better for geometry and reduced internal friction, but I still will use my "O's" until they give up the ghost, or I do.
Just my opinion -