Mk5 on last legs so away to build a mk6 crew recovery help

[ozzy69]

Hi need some info ! my mk 5 chassy is going soft everywhere so sadly after 3-1/2 years its time to move on and now have a solid mk6 06 crew chassy cab that i was going to cut the crew cab off but would like to leave it now so after a few days of searching on weights and lengths i think i have it wrong can i have a 14 foot bed ? Legally is this true going by 2 thirds and over hang etc