I think you're doing the right thing in playing it safe and applying for a visitor visa. It's a pain going through the process, but you should be fine, and you'll know before you travel whether you'll be let in as you'll have the actual visa rather than a waiver. I've no recent direct experience, but there was a documentary about the US Embassy in London recently, and it was clear enough that whilst they are tough, they are not out to penalise people unecessarily for things that at are at worst a technicality (in the sense you would have qualiffied for a visitor visa in any case). Being caught supplying inacurate information, is a big no-no for them, though and will imediately raise suspicions, so I think you're right to play it safe.
Whatever about being caught out for the overstay, where there's no way of knowing what records they may have (or absense of records that should be there), there's no way from what you say there could be any record of you having worked there, so I would be inclined not to say anything about that. Whetever you decide, though, by applying for the visa, you will know before you travel where you stand.