Hi there, I have a 1973 350 motor, it siezed on me, i have now a 403 (1978), i want to put 64 cc heads on the 403.(its for a stock car) the heads that are on my 350 do not have a visible casting number just below the valve covers, they do have a #5 on the left hand lower corner of each head. I cant at this time pull the valve covers off to check for other casting numbers until I get it in the shop. any ideas asto what these heads might be?

Thanks Ray

 

You don't have to pull the valve cover to find the casting number. It is buy the center exhaust ports. Not a SB expert, but I think #5 are 1969. Maybe #403859?

 

Sorry may have posted wrong number. The number I listed was 1970,1969 is,397742

 

Thanks 442harv, I took brake clean and a scraper to the area where the casting numbers should be, I looked up some pictures just to make sure and they are not on these heads, I am in Canada and maybe they came from a different plant or something. the cast numbers as far as I can tell have never been there

 

5's are rumored to be the best SB heads.

C's are rumored to be tbe best BB heads. (well best that are affordable)

 

#5 heads were used on all 1968-69 350 motors. The early SBO heads (#4, 5, 6, 7, 7a) all flow within a few percent of each other in stock form. Any would be a good choice.

 

Thanks for the info on this, I will be pulling the heads soon and I hope to find some casting numbers, but from what you all have said these are the 64cc heads i want for my 403.

Thanks Ray.

 

These will be between 68-70 cc's from the factory.
Fact of life, only early 330 chambers were ever that small.
Remember, you will need to drill the head bolts to fit the 1/2 bolts (17/64ths bit), and open up the left alignment dowel to 5/16ths".
The 403 intake valves would help, as would new guides.
Jim

 

My engine number 557752-b3 says it is a 78-80 350. My heads also say "GM5" also there is a (looks like) a pmv right below the dipstick, Are these good heads?