The OP was told at the time of purchase that the 1970 Dart Swinger he bought had a number's matching engine.
So far all we are sure of is that the OP bought a 1970 Dart Swinger with a 1970 model year 340 motor.
Is it a LL23 1970 Dart Swinger with a 1970 340 engine?
Is it a LL41 1970 Dart Swinger with a 1970 340 engine?
Is it a LM23 1970 Dart Swinger with a 1970 340 engine from another 1970 Dart Swinger/Barracuda/Challenger/etc.?
OR does the OP have a LM23 1970 Dart Swinger 340 model with the correct 1970 340 engine with matching VIN number.
I'm not trying to make this post a Numbers matching post but until the OP confirms that the Dash VIN is LM23HORxxxxxx and the number on the engine pad matches ORxxxxxx we don't really know if it's a 1970 Dart Swinger 340 car with a Numbers matching engine. (Trans also)
IMHO Any numbers matching vehicle should command a premium price over a non-numbers matching vehicle.
More important question is: Did the seller misrepresent the vehicle and charged the OP a premium $$$?
@F/A Tech
To the OP do NOT post the entire VIN anywhere on the internet.
Just let us know if it is a LM23 Swinger and if the engine number matches
Thanks