What casting number is it and what plugs to buy? short rope or long rope?, I don't identify the last digit, 10066036 or 10066038

[Javier tadeo]

 

[Gary S]

I'd say it is 10066038. If it has the factory heads, I would use the GM recommended plugs, likely the R45TS which was the standard plug for 350 engines with HEI for years.