Rob, you get shot at from three directions:
1) Appropriate driving licence category
2) Appropriate Road Fund Licence
3) Appropriate Insurance cover
Even with the correct insurance cover, if you don't get 1 and 2 right, the insurance may be invalidated.
I was under the impression that historic road tax does not allow you to carry a load, be it your own or for hire and reward. If you tax a hgv as private, you can carry a load subject to full HGV mot compliance. I guess the same would apply to a historic vehicle too, but you might need a different road fund licence?
I'm not aware that your question of whether you can tow or recover a historic vehicle with another has ever been satisfactorily answered on the forum. It would be very useful to know.