Sanity check: Decoding VIN for '69 Dart GTS

Hello Fabo folks - I need a quick confirmation to help me authenticate a local car that I'm considering buying.

The car I'm looking at is a 1969 Dodge Dart GTS with a 340/4-speed. The owner recently passed and the executor of the estate is now looking to sell the car. It's exactly the configuration I am looking for, but I'm suspicious that it's a clone based on the VIN. The car looks top to bottom like a GTS that came with the 340 from the factory. It's got the hood bulge callouts for a 340, the GTS badges in all the right places, and everything down to the backup warning light under the dash to the steering wheel and trim look legit, original GTS. However, the VIN: LH23B9Bxxxxxx looks like it was originally a 225/slant 6 car. I could not get under the car to see the VIN on the engine because the headers were blocking it, and the car does not have a fender tag.

When I compared this VIN to several of the VINS listed in the GTS registry, I noticed that all of those listed there start out with LS (special price class), not LH (high price class). In looking at a few of the public domain decoding sites, it appears that the car I'm looking at is probably not a factory 340 car, and may not even be a GTS at all.

The GTS 340 is a wonderful, underrated little muscle car that people are just starting to appreciate. They seem to be going up in value, but I'm still a little surprised that someone would go to the trouble of cloning one. So, I'd really like to know what I'm getting if I do decide to buy it. It's still a sweet car, but I'd much rather hold out for an original one than buy a clone at any price.

If anyone can offer an expert opinion to tell me exactly what this car is (GTS, GT, Swinger?) and what kind of engine it came with (was it actually a slant six?), it would be much appreciated.