Paul: I've ditched the M4, M36 and variants ideas, no sense in using a slighty inferior chassis for the same punch (and the T-34 idea too, for the same reason). I'm still thinking though about a makeshif SPG. Altough not a 128 mm PaK 44 because I think that at 10 tons it would had overloaded the chassis (Besides Trumpeter offer is both hard to find and kinda expensive here

). A PaK 40 or 43 sounds more reasonable from a technical point of wiev, and also a M101 howitzer, 25 pounder or a ZiS-3, for a captured 'flavor'.
Frank: Was my first idea, but it's rather boring (the munitionspanzer) and I already have Dragon's Bergepanzer IV in my stash. About any other combat engineering vehicle, to be sincere,I'm too lazy at this moment to think and scratch all the associated stuff
Maultier: Me has leido la mente ajajaja. I'm about to buy a -tamiya Panzer IV D to try the hybrid idea. The turret itself seems to comply with the available plans (PanzerTracts 4), and its lack of detail doesn't worry and/or can be fixed rather easily. The gun worries me, wrong proportions and lack of details. I have some KwK 37 spares from a few Dragon models, but upgrade it to a long KwK 40 it is out of the question (I could scratchbuilt some of that though, but it would still miss the barrel and muzzle break.)
Probably, If i continue with the hybrid Pz IV D/J idea, i would paint it in a distinct 'soviet' green, without rommelkiste or schurzen. The background history would be that one of the re-nascent post war central european armies (think Poland, Bulgaria or Czechoslovakia, or even Yugoslavia) used the turret of a former training Panzer IV D tank left behind by the NSKK or the Polizei and installed it in a less wore out Ausf J hull. A quick and cheap solution for the war ravaged countries and, of course, for my wallet.
Thanks for your ideas and insights guys!
RZV
PD: I managed to get a Tamiya Wirbelwind turret, could use it too...