Hi,
I also have a Brooklands roadster purchased from Russell, but I live 150 miles further north from Perth. I make this run regularly , in the Morgan, , my wife's hot Golf and our BMW. I'd avoid the A1 and the A 68 like the plague. The A1 is very slow with heavy goods and the A68 also and littered with speed cameras.I'd use the M11,A1 much of which is now A1(M) , A66 ,M6, M74, M73, M80 and A9. ( watch the average speed cameras on the A9) . Alternatively the M1, A1M ..........
You'll find the seats in the Brooklands very comfortable for long distance and the 3.7 performance awesome . I personal think the 3.7 if you drive it enthusiastically to be a tad underbraked, morgan should really have put discs all round and four pot vented on the front .