Was looking at a 1970 RM21 hemi car yesterday. It was said to have the original motor in it. It has been owned by the same person since the early 70's. The only number I was able to get a picture of was on the top boss. I am not familiar with what is or should be stamped here. It looks like the number has a G in front of it. Does this ID it as a '71 motor? What do these markings mean?

That is not a run of the mill stamping. In 1971 there would have been very little stamped on the upper pad, usually just WT for Water tested, and other small letters and numbers indicating machining details. Also, if the color is true in that pic, the paint looks to be of 1968 and the earlier "Race Hemi Orange". It makes me wonder if it's an earlier engine with day two stampings on the pad added by someone (machine shop etc.). Another possibility is a warranty replacement engine which sometimes had unusual markings on the pad. At any rate, if you want to really know the answer you'll need to look at the VIN pad on the forward lower side of the passenger side on the block.

Typical Hemi Vin stamping

I am headed over there tomorrow to drop off some parts. I will try and get some shots of the rail. So you are saying that the stamping looks done by someone/someplace other than the factory? The numbers and the "G" look almost factory in nature.

Even though it has had the same owner for over 40 years, it was raced by the dealership prior to sale and was damaged pretty good at that time. It is going to take some sustained effort to get it back into shape. If the motor was treated anything like the body, it most certainly could have sustained a variety of issues that affected it negatively. It is said to only have 28k on the clock. Overall a totally cool mopar... Glad just to have got to see it.

I'm guessing here because as I said, it does not look typical, and if you look closely you'll notice that the WT stampings have orange paint on them while the G and following numbers do not, that and with your added comments I'd guess the G and following numbers were added later, likely by a machine shop or the dealer. The VIN stamping will tell you if it's original to the car, The MN# stamped on the oil pan rail extension will tell you more about it's original assembly date and sequence, etc.

Typical MN Stamping Picture

also check the top of the block where the trans or bellhousing mates the block. Bring a mirror. If it is a 68 block there may be 's there rather than on the side of block.

That is strange. It definitely isn't a '66 or '67 used motor as the pads are stamped differently. My guess is that it's a later block or service block that was restamped with the VIN. The presence, or absence, of the numbers in Scott's photos should determine which. I've attached what a '68 bellhousing stamping looks like.

When Hemis were very plentiful in my part of the world and a hemi went to a rebuilder, the rebuilder would sometimes put a serial number on a motor to mark the parts. You have to remember a lot of hemi motors do not have serial numbers on them. The marking of a serial number on the Pad on the front of the block is easy to recognize for the assembler. I know I have marked the rods, crank, balancer and other parts so when I get it back I know the motor has the parts in it that I gave them and not someone elses parts. The number on the pad is it the number on the VIN Pad.

The OP's pic does not show the factory partial VIN stamping that should be present. Those numbers were added at some point after production. Scott's pic shows where the factory stamped them in '70.

"G" could be the plant code. Is the car RM21R0 plus the digits on the top pad : G193539 ? (answered below: NO)

I do not see an assembly dates on the pad either. Makes me wonder if this is a replacement block and that is why the serial number was stamped on the front pad.

Dan did you look at the last email I sent you with your weekend home work. I had a bigger list but can not find it, hope this can add something to your information.

Yes, I received this weekends work assignment. Typically NO dates on the HEMI top pad for 1970. Just the "WT" which this one got twice.

I have a 70 Hemi block in the basement but it is decked so nothing on the pad at all. Have to go and take a look at my 1971 Hemi motor out of the Cuda on the floor in the garage and see what is on it. There was nothing but the WT on another 1970 Hemi Block I owned that was an over the counter block that I sold. All the 1966 Hemi Motors I have owned or own have the Letter on the motor, the "B" for the year.

Went out in the garage and took a look at the 1971 motor. Just like you said Dan, WT on the pad also an A. Will have to see what Chrysler says about that A.

Here's a 70 Hemi pad, WT and misc. stamping numbers on the pad were the norm on 68-71 engines.

Same engine VIN Pad (goofy stamped VIN #S like this were pretty common)

Same engine, casting date

Here's a 68 pad, block was cast in 1966

Crawled around in the mud today and got some shots of the VIN pad and pan rail. Kind of a pain due that and the big ole rusy headers in the way. I think some of them turned out. Also got 833 stamping. It is original to the car. will post in a few....

VIN pad

Pan rail

I would say what you have there is a service replacement engine, could have been installed under warranty, or just purchased over the counter.