I've been doing a comparison study of the two kits also. It looks like the '72 body WOULD make a good donor for a '70 convertible. the bumoer profiles appear to be the same with some very minor filing to make the two kits work together.
The front of the hoods or completely different so you need to use the '70 hood with the '70 grill
The tail ight openings are also different, so you need to use the '70 rear bumper too.
I don't know if you noticed, but there would be a lot of modification needed to the quarter panels to make the Johan '70 442 hardtop into a convertible. There's a lot more to it then just chopping off the top. That's why the '72 makes a perfect candidate for a '70 Oldsmobile convertible.
I'm curently waiting for some parts from the Modelhaus. Since I want to make a '70 Pace car out of the '72 body, I orgered a '71 grill for the johan '70.
I hope this helps, MIke
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