What block casting and date numbers would have been used for a 1969 427 390HP that has a body tag number of H10? (H10, I believe is April 10, 1969. ) Are there several block possibilities? 2 bolt or 4 bolt?

Thank you for the help!

 

So far I believe these are three possibilities:
3935439
3955270
3963512

Would there be others and I'm assuming the casting date would need to be before the body tab date of April 10, '69. Am I on the right track?

 

512 is late 69 So you probably can eliminate that one. Mine is Oct 69 and I have a 512 block. It was also used in 1970 as a 454

 

I found two bbs with numbers that would work. One has a date 10 days before the body date and another 2 months before the body date. Which date would be more correct?

 

Steve,

The casting numbers that you listed were all used during the 1969 model year at various points in time... 3935439 was used very early in production for all applications (both two and four bolt main)... 3955270 was also used relatively early in production (two and four bolt main applications), but is the least common of the three blocks used that year... 3963512 was the final casting used (also in two and four bolt main applications).

Your 1969 L-36 with an April 10 body tag date would almost certainly have used the 3963512 block which fortunately is the most common of the three... It was used in all Chevrolet applications that required a short deck 427 so there are a lot of them out there. Typically, the block would predate the car by about four to six weeks (in an L-36 application) although both NCRS and Bloomington Gold allow for as much as a six month lead time in their judging criteria... Mainly done to account for factory "anomalies" in the production process.

The L-36 and L-36/L-68 applications in 1969 used a two bolt main block although there is at least one instance of a factory installed four bolt main block.

Larry,

Be careful... "Early" and "late" are relative terms here. Yes, the 3963512 block is considered the "late" production block, but it was phased in as a two bolt application around October 1968 and as a four bolt application in November 1968 if my memory serves my correctly... For the most part, it was used for the majority of 1969 model year production.

It was also used for 1970 production (as you noted) as well as 1971 in all Chevrolet applications that used a short deck 454.

Regards,

 

I've discovered that the H10 on my door jam tag would be March 10 rather than April 10. Can someone confirm this? They started production in Aug 68... not Sep 68 like I earlier thought. Correct?

Both blocks I found are 3955270 4bolt mains.
The earlier one (with casting date of Feb 10) is the one I believe I should be going with.

 

Steve,

You are correct...

I went back and checked my references and "H" does represent the month of March for the 1969 model year.

The date is just about perfect for your particular car... Of course, your L-36 would have used a two bolt main block, but that is practically a non issue once the oil pan is installed. As I mentioned, the 3963512 block is most common and would probably be the one that was used, but the 3955270 casting is perfectly acceptable (although you don't see it too often in Corvette applications).

Nice find!

Regards,

 

OK... I'm sorry... I just assumed that they(512 block's) were late because I've seen some 69's made just a little earlier and they didn't have 512 blocks. I also have 3964290 heads which are not listed in the "black book" until 1970. My heads were cast in August (like most of the cast parts on my car) and I have a mid October 69 car. I also have the left valve cover with the wire stand-off moved forward but it still has the dripper finger bump. Strange cars ... these 69's My car seems to be a mixture of late and early parts..Maybe my car was a put together car but I don't think so. Geeze I hope not anyway


[Modified by Larry B., 9:03 AM 6/29/2004]