Today, dollar for dollar, is the 318 faster than the 340 ???

Did you put a bore gauge in the hole or just eyeball it? There isn’t any cylinder I would run today that was any factory bore. Crosshatch means nothing because it’s most likely wrong for today’s rings. Factory bore geometry was horrible. That’s why you bore a cylinder. To get it correct, and the factory finish was marginal in its day. In fact most guys today don’t measure their finish and they have no idea how much they could improve the finish if they measured it.
If we are talking "modern" engines yes, the old La is more forgiving. The Ford Modular V8 ,for example is easy to screw up, with home and or old machine shop techniques. The tolerances and machine surfaces are much more minute and specific. I have seen a Ford 4.6 where the head gasket wouldn't seal because of .001" imperfection on the deck surface. On an old cast iron engine (such as he LA) if someone chances a home hone and re ring what's the worse that will happen? oil getting past the rings? it will be obvious, then pull it out and get it bored. If the rings seal and there is compression it can be ran, how many actual miles a year are put on a Classic car? I venture to say car show guys "might" put 10 thousand miles a year on their engine on the other hand if you are racing the engine and want "blueprinted" clearances, than yes go all out . for a classic car show guy to dump all that money into an engine he wont wear out, hes just leaving it ( the money spent on all that blueprint work) for the next guy to get for cheap.