HI!
I thought, that distributor can be original, because those are quite realible,has it contact caps, or is it electrical system? Have this block a coolant water output under the inlet manifold, and where is the crankcase ventilation system? is it in the block or head cover? If someone hasn`t modified burning room it is smaller than 398, and IF engine is B-23 it doesen`t fit good because cyl. dia. and the cooland holes are too small. All 160 heads are so called SCP-core. 398, 405 and 530 has both types. only 531 is allways BCP core. In the high pressures SCP:s can usyally crack. However if the engine is runnig OK those broblems doesent matter anything. If you mean VOLVO`s Monotester sysem, which lies in the valve cover, it doesen`t tell anything what is the engine`s size. ( in overseas modell i`m not sure)In here its all B-17-23 engines. Hope you get all broblems worked out.

Yrs:WEBERMAN.