No idea who does tractor insurance but Adrian Flux would be a good first port of call.

You need category F on your licence to drive a tractor.

I’m sure a Google will give you more info.

Edit: Have you been watching Car SOS?

Afaik you can drive it on a car license, certainly that’s all i have ever had, and i come from a farm which ran slightly later 35 diesels, both 3 and 4 cylinder engines.
And, will it need to be registered so you can get a number plate?
T20s were taken to the south pole iirc. Rev limiters were raised from 2000 up to 3000rpm at altitude on antarctica, I’m pretty sure i read that somewhere.
I’d quite enjoy some pictures.

Full licence would be fine though depending on your age you may need a trailer test to do any towing on the road. Insurance and a number plate also needed, it was common for older tractors not to have a v5. You don’t need an MOT but it needs to be in a roadworthy condition.

I always wanted to drive a tractor around to hold up all those drivers that get frustrated at cyclists holding them up 🙂

I would go got a Lamborghini tractor though just because.

NFU is a regular port of call for non standard insurance. Should understand tractors at least! Otherwise I guess the owners club may have deals / sponsors. Adrian Flux insure stuff but IME were pricey. Other mates got better deals from NFU. YMMV.