As it appears in your pic I'd say you have a non stamped block. I wouldn't stop looking just yet though, go a little further in each direction with your paint removal to be sure. I can see where a line worker may have stamped it only on one part (as opposed to both) in the case of an automatic car since they would be right next to one another. On 4 speed cars the trans stamp is in an entirely different area of the trans hence my earlier comment about finding one on the trans would mean the engine would also be stamped.

*BTW, in case you didn't already know, your engine should be the turquoise (same color that's under the current orange).

All of your other engine stamping codes (dates, etc.) align perfectly with your cars SPD, I remain confident that it's the original to your car. I can't say for 100% certain without a personal look but otherwise everything looks right.