Lee,
Don't know if this will help in the UK. I have a 351/408 Windsor with AFR 205 heads and I have a Griffin radiator. It is 3"x19"x26" top entry and bottom exit with a steep slope toward the front. Those are my inside measurements. I run an electric water pump(return to engine) of 35GPM flow and on cruising I don't use the dual radiator fans at all. Only if setting at a red light, or constant stop and go traffic. With air temps even in 90 degree + range the temps stay in the 150-170 degree range. I have a thermostat at about 150 for the water pump only, for if I forget to turn them on manually. Guess why I added that!! Mine has been in for some time so call them for a quote.
Bill