Initially it looked good but now it looks (to me) like more of a hodge podge. It would have the later thick tires but early D type hub caps, and oddly a Panzer IV F drive sprocket so it can use the later 40cm tracks. At the Nats they showd some other conversions like a Panzer IV F/G but it seemed just to be a new gun barrel for the Tamiya J to make a cosmetic F.
There is more to that conversion than 'a new gun barrel'. The J turret was modified on its front face and roof, and side doors and pistol ports were added as well as provision for fitting the early-style . New mid-series road wheels are included along with a new drive wheel. On the rear I've added the smoke candle rack and turret traverse muffler, while I include a mounting step for the left side. There is, as you noted, a new gun barrel as well as the unique ball-shaped muzzle brake.
Maybe you should have taken a closer look while you were there; that's why I brought the example along to the show. Anyways, since you missed some things, here's a photo.
https://mail.google.com/mail/u/0/?ui=2& ... &safe=1&zw