Thank you a lot about the information, after some searching of my own and I will return with new comments.
After research, I found the RB.141 Trident seems equivalent with the Boeing 727-100. The Spey Trident was underpowered, especially the 3B .The RB.140 Trident is a Spey Trident 2E in capacity.
The most balanced Spey trident is the 2E, with 2.66 Imp. Gal/St. Mile and the 3B rises to 3.747 Imp. Gal/St. Mile, while the Chinese 3B has 3.158.
The Trident was first thought to be equivalent with the Boeing 727-100, so the 2E seems to provide the fuselage, wings from Avro 776 and of course triple Medways with 42,000 lbf thrust. This combination perhaps had more fuel capacity from the Spey Trident 2E (if is same with the B727-100, 6730 Imp.Gal, and with 2.66 from above) range would be 2530 St miles. With the wing tanks HS.800 has fuel rises to 8730 Imp. Gal, range perhaps would be between 2900-3150 St. Miles. With larger wingspan, fuel capacity could be even greater.
An development of that Trident would be similar with the B727-200, with the 17000lbf Medway.
Finally I have the HS.800 above the Avro 776 for comparison with some notes. Wingspan calculation is uncertain. Also the HS.800 has larger fuselage and bombay. I have also the wingtip from VC.10 for comparison with that on HS.800.