Is this the correct motor for a 72?

[Myasylum]

This is the number on the block...
3698630-400 3

Is this a 73 block? Is that possible for a late model 72?

 

[moparmarks]

There should be a casting date on it. The 3 means 3rd casting from that mold.

 

[Myasylum]

Oh? You know where the casting date is?

 

[QuickBpBp]

Check next to the motor mount ears...

 

[33 IMP]

Casting date should be straight above the casting number you showed. If it is the original block for your car, your cars last 8 or so numbers of the Vin should be stamped on a pad just above the oil pan rail. (Typically 2(letter for assy plant)xxxxxx) The "2" would be for a 1972 car.
Edit: Quick bp's location info is better than mine.

 

[moparmarks]

Yep on the drivers side is the casting date and also in front of the pass head is a pad that should have some stampings.

 

[Nacho-RT74]

And no, you can't get back in time with a 73 engine on a 72 lol. It is posible backwards thought. Remember 73 model production began on mid year 72

 

[ODZKing]

73-78 block according to what I find online. However (and I am guessing here) I would say since the 3 indicates a third cast/mold it is a later block. If the date code is 72 then I stand corrected but many things could have happened when or shortly after the car was purchased. Small crack in the block (leakage) would have prompted the dealership the replace possibly months after. Who knows, but again that is my guess.

 

[Myasylum]

Yea, I guess according the the markings on the distributor is a '74 which really sucks.