Thanks Curt B. I guess for now I will start the engine and watch the temperature gauge. As I mentioned earlier I hope to only have to run the engine for a few weeks until the original 235 is rebuilt and back in the truck. At that time I may take the head off the 261 and inspect it.
I just wish I could confirm the head casting numbers (3835913) were used in 1959 261 engines. There are some other numbers on the left side of the head which are GM13. Also the right side of the head has the number 18B followed by a 913 which sits above the number 241 which sits above the number 670. Any help with those numbers would be appreciated.
