Theres no way the VR38DETT is only 109lbs heavier than the SR20DET, PD's engine weights seem to be way off
And the VR30 is ~430lb... Similar argument could be had that there's no way the VR38 weighs 180lbs more than the VR30 it was derived from and very closely related to. So you have to ask what makes the VR38 so heavy on paper, and is it an accurate figure to go by? Don't forget that 608 lbs includes the forward diff which won't be included on a rear drive conversion... Also possible PD have opted for a weight that doesn't include a bunch of unnecessary engine driven ancillaries such as aircon & power steering pumps.SR20 is 328lbs w/o transmission.
VR38 is 608lbs w/o transmission.
I think you're reading into these weights too much (or not enough, idk)