alright fellas,im in the middle of doing a reshell,but want to know the LEGAL way of registering.

basically my cars shell is fubarred to the max with rot, so ive bought a very mint shell on a Y plate where as mine is an A plate.
the original shell has a private plate which i want to keep ,but the original cars last lot of tax and mot ran out in june 06

the new shell needs paint but im undecided as to which colour to go for

what i want to know,is what is the legal way of doing things??? i dont want the car to be Q-plated but everything bar the shell and engine are going to be off the original car etc,and new for old parts as and where reqd

ive been told i can do a change of chassis no on the logbook to coincide with the old cars registration,but im not 100% sure,and dont wanna get screwed in the end

any help will be muchly appreciated

cheers
stu