Its not quite a D-28 minus the trim. The bracing is different as in “A frame” instead of standard X and its got a M/T neck joint instead of the dovetail. Actually closer to a D-15 structually. Not that that’s a bad thing. Just different.
The Custom MMV was the first Martin I bought several years ago. I picked the best one out of the three that GC had in stock. It sounded good and I was really proud of it but it was no D-28. I sold it after a year to buy another Martin and have bought and sold quiet a few others since then before settling on the two I have now, a D-18V and a '78 HD-28.
As I stated, its a nice guitar but for $1400 I’d be looking for a used standard series D-18 or 28. Just my opinion from my own personal experience. Good luck hunting and enjoy whatever you get.