The Canton adaptor is a bit thicker than the factory plate, so keep that in mind when buying your filter.
I use a K&N PS-2004 on my 340 with the Canton plate and Doug's D453's, it clears everything just fine.
Amazon product ASIN B0067ECW72
That filter is also used on 2000's Dodge Ram 2500's with a 360, and even a 496 Chevy big block that comes in some buses.
I have also used this filter, although with the Canton adaptor plate it's a pretty tight fit to the Doug's. Not sure how that would work with TTI's, might be fine, but I don't have a set of TTI's
Mopar Performance P4452890 Mopar Performance Oil Filters | Summit Racing
Yeah, no. The spring in the filter is not a bypass valve that bypasses the filter at a certain engine oil pressure. Sorry. It's there to bypass the oil filter if the filter plugs up, not if the oil pressure in the engine gets too high. Two different things. The bypass in the filter is set up on a pressure differential between the engine oil pressure and the pressure in the filter, and it closes if the filter plugs up to keep oil circulating through the engine.
There's a pressure relief valve in the oil pump that opens past a certain pressure, but that doesn't bypass the oil filter.
Both the TTI's and the Doug's headers for small block mopars work just fine without the 90° adaptor, and those are pretty much the best headers available for these cars unless you're having a set custom made. As for the rest of your comments, yeah, the oil filter I linked is a factory size for MUCH bigger engines than the OP's 340.
Something to note as well, just because an oil filter has a larger body does not necessarily mean that it has more filter material. There are larger, cheaper filters that have less filter media than the one I linked to. Bigger doesn't always mean better, the amount of filter material is what you have to pay attention to and it's not alway a direct link to the external filter size.