First off, congrats on your new toy.
You are correct that the GT in that year had more bling, but the boat itself is still the same. They all had the same windshield, build structure, etc. Not the for sure answer, but using google, the 4.3 was offered in carb or MPI, where the GT came with MPI. I'm sure you could have ordered the MPI on the MX. Changing a carbed engine over to MPI is not easy or cheap, so I doubt that was done.
It's really no different than my 2016. In that year, they offered 3 versions, GTX, GT and GTS. All the same boat, except different levels of features and fancy bling. The GTX base model could be ordered with just about anything, where the GTS already had the full load. We chose the GTS that already had all the upgrades, nicer upholstery, different gauges, stainless fittings, etc.
I suppose the only true answer would be to ask the manufacturer for a build/spec sheet for your boat.
Regardless, enjoy that new toy.