Years ago I was thinking about putting a V8 into a Miata. The insurance company back then said they didn't care, but they would treat it like a regular Miata. In other words, if I totaled the car, they would only pay as if it was a normal model not the extras.
I have Travelers now. I asked my agent what my premium would be for a Mustang GT manual. I expected it would be higher than my current car. Nope, the insurance for the same coverage was less for the GT.
I had a 71 with a 351 Windsor and a 90 GT. The 71 was an auto and the 90 was a manual. I am tired of driving, so I will be buying a 2019 GT with the 6 MT. It will give me something to amuse myself with.