Like many others, I used the TFP Airachnid head and planted it onto BH DLX Starscream body and start from there.
I clipped out the front & rear elevators/horizontal-stabilizers, used a junk umbrella to do the spider legs and used some plastic sheets to reconstruct Airachnid's hip area to a more cartoon accurate design.
I also removed the main wings and replaced the 4mm rods into the standard 5mm rods as handles for the cleaver (?) weapons. Obviously, I also enlarged the holes on the fuselage where the wings are attached to 5mm...although I don't see the point as it makes no sense to transform it into airplane mode...but I do like to have the option