Engine:
Here is the # found below the #1 spark plug: AL-HP-187431C
Here is the casting #: 2463430-15

Tranny :

A-904-G, and I found 3 serial # on it, one is 2464935 4 and the other are just above the pan: 2466119W 1552658, these last 2 have a space between them.

So what do these numbers have to say?

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1965 Valiant Custom 200, 2dr hardtop, 225ci
1997 Monte Carlo, 3800 supercharged swap
1995 Lumina, 3.4 DOHC swap

Means a 225 engine originally installed in a 1965 Canadian-built 111"-wheelbase Valiant. The 187431C may be part of your vehicle's VIN; I don't recall and my '65 Canadian FPC is far, far away from me.
Means a pre-'67 RG (225) engine block.
Means a 1965 A904G installed behind a 225 in an A-body.

All in all, sounds like you're working with the original engine and transmission.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan!

I checked but the 187431C is not part of my VIN, so I don't know what it could be.

Can I ask wich letter means what? I searched but didn't find

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1965 Valiant Custom 200, 2dr hardtop, 225ci
1997 Monte Carlo, 3800 supercharged swap
1995 Lumina, 3.4 DOHC swap

A: 1965
L: 111"-wheelbase Valiant
HP: High Performance (225 engine option rather than standard 170)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.