If you're not intending to to keep the truck absolutely stock, it would be better to go for one of the 1/2 ton models, these have the best range of "bolt on" disc brake, power steering conversions etc. available from suppliers like CPP and Chevy Duty, not so much in the way of upgrade parts available for the bigger trucks "off the shelf".
One other thing, have you thought of buying in the USA instead of the UK? IMO, you'd have a much wider choice, and would almost certainly pay less money for your ride if you take a trip over, buy yourself a truck and ship it home -even after you've paid for the shipping and UK customs duty. I imported my 1950 truck from the US in 1995, my brother has imported another three trucks since then -also every one has come over loaded with spare parts.
Best of luck whatever you decide on, Stuart.
Last edited by Stuart_Giles; 10/18/2011 5:21 PM. Reason: more added.