Building a D-30 fro Incoming Campaign. Buil is almost complete, can't decide if I want it in towed or firing position. If I do it towed, what is the standard prime mover for the D-30, GAZ-66 or Ural 4320?

In fact, it depends of the potential danger and/or the unit. If there is a significant danger, then an armored prime mover will tow the howitzer ; the standard armored prime mover is the MT-LB, as depicted in the SKIF kit. If there is less daner, or for a long distance travel on roads, the D-30 can be towed by a truck. The most probable trucks are either the Ural-375D (or a -4320) or the ZIL-131. There is no way that a GAZ-66 can tow a D-30 as the max towing load is 2000 kg and the D-30 weights 3210 kg in travelling order (3440 kg for the Yugoslavian D-30J)
Sources :
Jane's Armour and Artillery
Janes Military Vehicles And Logistics
Soviet/Russian Armor and Artillery Design Practices : 1945 to Present

Hope it helps.

That is what I thought. Guess I will have to use the GAZ-66 for something else and probably put the D-30 in firing mode. Thanks.

If you really want to use your GAZ-66 for fire support, you can try to convert it into a BM-21V Grad-V. It is a lightweight version of the BM-21 MRL for the airborne troops. The BM-21V has 2x6 122mm tubes mounted on a GAZ-66B. The GAZ-66B is the airborne version of the GAZ-66 with collapsible canvas cab, removable doors and windscreen, telescopic steering wheel and tie-point for parachute dropping.
It seems quite a conversion, but it can be a nice one to do.