[GtoFM]

I met a vender, a Chevy guy, at the Detroit Swap Meet today. He bought a '69 Judge project car from the second owner who rebuilt the replacement engine. He has PHS docs to validate the car. The PO is in his 80's and cannot complete the restoration. The PO couldn't remember the details of the engine rebuild other than the block is 'special'.

Engine details:
9778791 D 31 4 (421 CI Cast April 31, '64), There is no Engine Code on the right front other than XX.

Since the 421 wasn't in production until '65 and this was cast early '64, could this be a test block?

Other interesting notes on the date code. The D is upside down and there are only 30 days in April. This could be human error.

I found a 2016 thread RE: the XX stamp with no resolve. This block is also missing an Engine Code stamp. Any thoughts?

[b-man]

Well I have a 1964 421 HO engine (code 45B, manual trans HO) in my Le Mans so 1965 definitely was not the first production year for the 421. 1964 421 block casting number is 9773157. All 1964 V8s had a 3 character engine code, 2 numbers followed by a letter.

Your 421 block casting number 9778791 is an early 1966, 9782611 is a late 1966 421 which was the last year of the 421 production.

The 1963 421 HO is basically the same as a 1964 HO, both have the same 9770716 heads.

Then there’s the 1961 (over the counter only), 1962 and 1963 421 SD engines as well.

[242177P]

Originally Posted by GtoFM

Other interesting notes on the date code. The D is upside down and there are only 30 days in April. This could be human error.

An upside down D is still a D, but a backwards one? That could be a G, and July has 31 days. July 31, 1964 --> 1965 421. Assembly line was winding down, they'd finish the car builds just two days later. If the plants didn't already have all the motors they'd need, built and ready to go, I'd be shocked.

So what's the foundry doing? Those assembly lines are going to be up and running again in just 23 days. The whole on-time inventory thing everybody is doing now (Yay, supply chain difficulties!) simply wasn't done back then. Disruptions would wreak havoc on an assembly line. Is it an early date? Yes. But a prototype? X to doubt. Hope this helps.

[Kenth]

1961-62 421SD block #538181

1963 421 block #544988

1964 421 block # 9773157

1965-early 1966 421 block # 9778791

1966 late 421 block #9782611

[GtoFM]

Thanks for the corrections and clarifications guys.

I should have said the '9778791' 421 wasn't in production until the '65 model year.

The upside-down D looked very clear, but I'll see if I can get another look.

So, the questions remain, why no 3-digit Engine Code and what does XX represent?

[lust4speed]

What if the shortblock was purchased from the dealer parts department? Wouldn't the replacement block be lacking the front codes? Later on we had SR blocks, but maybe that started years later? Maybe the XX was added by the dealer as their method of identifying a replacement block.

[421 Bird]

I had a '65 421 motor from a Bonneville. The block was a 9778791 YH code. It also had the XX stamped on the front of the block. I was never able to find a reason for the XX stamping.

[Verdoro 68]

Old thread on 421s with an XX stamp. It doesn't look like much was resolved, but there appear to be a few out there:
https://forums.maxperformanceinc.com...d.php?t=794054