Most Panzer IVJs seem to have had the vertical muffler pipes, but the Tamiya kit has the horizontal one. Any ideas for how to do the conversion to make it a proper Panzer IVJ? I know there are a few examples of Panzer IVJs that had the horizontal muffler, but they apparently all carried zimmerit, and I don't want to put zimm on the tank (I hate the way zimm looks on the Pz IV).

What else needs to be done to convert the tank into a proper Pz IVJ late? (35th modelers might also be able to help with this.)

Gaso.Line used to make a Jagdpanzer IV conversion kit which had the vertical mufflers and, hold on to your hat, PE Thoma screen schurzen. Perhpas you could email Olivier at Quarter-kit and enquire/suggest they make a conversion kit for the MKIV.
GLenn

Try this reply over at Missing-Lynx. It relates to the diferences between the Ausf H & J, but there is still some relevant info for the early/late J's

Panzer IV diferences