Interesting thing is that many US metal aircraft had the top of the tip just flat while the bottom rose up to meet it. Most model kits get that wrong. I do not think the P-38 was one of those.
I just checked and the P-38 DOES have the upswept undersides at the tip. By the way, before the J model the exhaust for the intercooler cooling air exited at the tip through a rectangular hole.
Also Lockheed was just about the only company that always extended the hortizontal stab out past the outboard fin/rudder. It is lot easier to do it like the B-24, B-25, Beech 18, Ercoupe and A-10, so I do not know why they did that.