Don't have my books in front of me, but the H model was the last version of the P-38 to have the shallow chin under the engines. In the earlier models the intercoolers were located in the leading edge of the wing, as the engine power increased through the H model they were no longer up to the task and that space was converted to extra fuel cells and they were put in the nacelles. This is why the J/L models have more internal fuel.
Basically you're looking at a plane that is between the G and J in weight but has the same engines that appeared in the early block run of the J series and had a WEP setting.
Like I said I don't have the info in front of me but it should be close the J in speed I believe and a little lighter.