No need to raise junk, when you can see a free flop.
You flopped top pair on an extremely dynamic board, and I much prefer to lead out here. My main goal is to just end the hand right now. The reason for that is, there are literally no cards in the deck, that are not bad for you, other than exactly a J or 6, which would give you two pair or trips. Everything else will either make trips possible, put a 1-liner to a straight, or reduce your top pair to second pair. And you are going to be out of position on future streets. So nothing good can come from letting him see another card, and this is why, protection is the absolutely main consideration here.
Its also worth noting, that leading here is NOT a donk bet, since he did not raise preflop. And for the same reason its highly unlikely, he has an overpair, because why on earth would anyone in their right mind limp BTN with 77-AA? That makes no sense what so ever, so while not completely impossible, we can weigh those hands down a lot. Which mean, that your 66 is close to the nuts right now, but will get a lot worse on future streets, if you let him continue.
You talk about turning your hand into a bluff, and this makes no sense what so ever. To do that, you would need to assume, that his range is mostly made up of hands, you lose to, and that would also fold to a donk bet now. And this is just not the case, because such hands would mostly be 77-QQ, and as I already said, he hardly ever has that, because he just limped preflop. What he has is complete air, that was trying to make you fold on the flop. Or hands that just improved to top pair or a flush, and those hands are not going to fold. So the only play, which makes sense now, is to check again and call most bets, since you have a diamond in your hand. But he checks back, so there is no decision for you to make.
You make a J high flush, and while you could lose to A or K of diamonds, or to 43 of diamonds, those hands are somewhat unlikely, when he checked back the turn. So I think, your hand is good enough to put out a small bet for value trying to get called by basically any kind of bluffcatcher. As played you have an easy call, when he makes a small bet.
The hand is a bit of a cooler, but what is way more important is to play spots like this more aggressively. There is no such thing in poker as "respecting the limp" or "checking to the preflop limper"