Standard P-38s only had two hard points at this time. 2000lb bomb load is two 1000lb bombs, not four 500lb bombs. If one point is carrying a drop tank then you get one bomb, pick size. Using more than two underwing stores increases drag and reduces range. The 500lb bundle of incendiaries each B-25 carried might have been an awkward load under a P-38.
Do larger than 150 gallon tanks exist for the P-38 at this point?
Is the 2000 mile range of the P-38 done at Ferry speeds with no allowances?
A P-38 could burn 2-3 times the amount of fuel per minute at high cruising speeds as it did at most economical cruise. This is not Military (5 or minute rating) but the 1 hour/max continuous rating or even less. Even a 1/2 hour at near 300mph speeds at low level could shorten the max range by 200-300 miles.
How fast to you want to fly from the east coast of Japan to the west coast and out over the water to get beyond the range of Japanese fighters?
The B-25s actually flew a good part of the length of Japan and not just cross wise.