Absolutely nonsense talked on this forum sometimes.
Right as someone who has done just about all that was asked I will give you a straight answer.
Bought a silver 75 diesel back in 2014 ish.
Brought it home as none runner, got it running. Then proceeded to do everything to it from my scraped 190 zt at the time.
Car ended up as a diesel zt, inside and under the skin with everything bar steering rack changed, including a set of black then silver hairpins. Only thing it lacked was the boot spoiler in mbb.
To insure the car standard against when it was converted to being a 75 cost me nearly £120 more than a standard 75.
However I also had a zt xpg diesel at same time, and it standard was going to work out the same as the 75 diesel standard, but again that was with green light insurance and at the time about 14 years ncb. I ended up selling it as I got a nice auto 75 blue saloon instead.
Again, as regards classic insurance, I've had dozens of my fleet on my classic policies since 2011.
Only last year did they limit me to cars must be 20 years or older, however they where happy to accept cars I'd already got on my policy (such as my LHD diesel auto 2003 or at the time my 2006 registered 1.8t).
My main 75 policy is a bit higher than needs to be as I've flux flex on mine giving me full comp coverage to drive any car or 4x4 or 3.5 ton van max for private purposes instantly as long as it already is taxed, mot and insured. Thats is £360 a year with mods declared Adrian Flux again.
So currently I have on my classic policy costing me £313 a year for 5000 miles between the cars with over 20 years ncb working as a ambulance responce driver part time and factory worker full time.
1998 216 convertible
2003 75 lhd diesel auto
2001 75 diesel tourer manual
2002 75 v6 2.0 tourer
2002 75 v6 2.0 manual
2002 MG zt 190
2002 MG ztt 190
2001 mg ztt 190
Only one I've not got on it is my 2003 1.8 which is on my main policy as of June this year as I move my 2001 white 75 saloon to Classic policy and then it's my daily for now.
And my track day / fia event cover for my 190 zt saloon is £75 a year with flux also for 3 fia sanctioned events or 6 private events. Hopefully actually get to use it this year without restrictions!