Insurance Hagerty/Grundy ??

Who insures the 64?

If it were me I would go Hagerty, they are pretty flexible IMO. Don't give them any voluntary info, just answer their questions. You will need a daily driver, which you have, with current insurance on it. They also require it to be garaged, and may ask for pictures. What I did was put my car in the garage and took a couple of it in there.

They don't have a problem with casual driving like Grundy did when I checked with them

You might get a discount if you put the A100 and the 64 together on a policy. You will also want to put a value on them, they will agree to it as long as it isn't way high, if it is they could ask for an appraisal.