I wanted to follow up with what I found.
I pulled all of the spark plugs to inspect, they all looked the same and typical. I used a plastic soda straw and found TDC on #1, the timing mark on the damper was basically right at zero deg mark.
Since all of the plugs were out, I figure what the heck, might as well do a compression check. This is where the story goes sour. All of the cylinders popped about 170psi, except for #4 and #6. Both popped 60psi. In fact, with the compression gauge on #4, I could hear and see it pushing back out the carb while spinng the motor over, and with it on #6 a wierd sound coming from somewhere, the exhaust I think.
I have no idea how this translates to wicked bad pinging, but it matters not. Either the head gasket is cracked between 4 & 6, or the head is cracked.
So now I'm on the hunt for a 60s/70s straight six to drop in. The SB 400 was a nice motor, but 8mpg was not particulary a virtue. A 292 six would be nice, but I hear the are fuel thirsty also. So perhaps a 230/250 is in this old truck's future.
-John
