It seems I have "accidentally" won an auction on eBay for a partially built Tamiya Panzer IV.

I'm now thinking about what I'm going to do with it and was considering converting it from an early production J to the more common H.
It shares the same main exhaust and still has 4 return rollers rather than the 3 on the late J so besides the turret rotation exhaust (which is missing) what else would need to be done to a Tami PzIV to change it to an ausf H?