I might be speaking a bit out of school (I've only changed my head once) but that much carbon (on the pistons and the head) makes me think there's a lot of oil consumption/combustion going on. Inside that means worn rings and/or leaky valves/guides.
Did you put enough miles on it to get a feel of how much oil you were losing? If it was considerable (say well more than a quart every 1000 miles) I wouldn't just put'r back together.
Just my 2cents. And make sure you torque the head bolts correctly (proper order and torque) on the reassemble! This is what I did and have had great results so far. Here is the pattern I followed:
I did things in four steps, following the pattern each time.
Step 1: I just put in all the bolts with almost no torque just with a normal socket
Step 2: I used a 'Breaker" torque wrench and put on 50 lbs on each bolt
Step 3: I used a "bender" torque wrench and put about 61 lbs on each bolt. I made sure they could hold the 61 lbs for 5 seconds without moving. At least with my wrench, it was hard to be accurate. I had between 61 and 65 lbs per bolt.
Step 4: I rechecked all the bolts in order with the "bender" wrench to make sure they were holding at least 61 lbs for 5 seconds. I think 2 bolts needed additional torquing.
The PO said he had some motor work done but wasn't specific on what was done. His mechanic simply got the car running for him and gave him a bill, which was about $600 in labor so what was done I have no clue, nor did the PO.
) The plugs, especially in #2 were oily and I would change them every 1000 miles. The car, according to the odometer, only had 53,000 miles on it and over a two year period I put another 5,000 miles. As for oil consumption or leakage there was very little, probably half a quart every 2,000 miles. However the oil pan gasket and rear crank seal began to leak a bit. 