big decision...help needed, about frame swap

basically.....about a year ago i bought a spares ped so i could use it on my ped.(SPEEDFIGHT 2)
but a while before that i let sum twonk of a mate have a go on my ped and he smashed it to bits and bent the frame at the front...so now the inner panels dont fit on properly.
and the engine has also blown after that incident aswell.
so now ive got a new engine in it from one of my spares bikes but the other one has pretty much been left untouched.
however the engine that im modifying in my project topic is the one from the whole spares bike i have.
when i bought it he gave me only a small part of what was left of the logbook and the keys and a hand written receipt.

so what i want to know is.....should i transfer all my panels etc from my current ped onto my spares bikes frame and engine to use....but swap frame plates and say its the same ped as before?
OR.....apply for a new log book for the spares ped and get that on the road. As it will be that frame and engine ill be using anyway.

because the only thing id be using off my current ped is my numberplate and panels if i were to keep it registered as my current ped.
If i got a new logbook and got that one on the road i may even be able to sell my current ped as a whole and build up on the spares bike as my main project.
how easy is it to get a new logbook and get it back on the road?

sorry if it's a bit confusing imp:

luke

 

if it was me id change plates and say its the same bike because if you get a log book for the other one you got to pay to change ya insurance over tax and mot it and all that easier to change the plate over
illegal though lol

 

yea i suppose so.
however...if i made my spares bike road legal....id have two road legal bikes...so i could sell one of them...maybe get £400 for one when i've done it up a bit.
and its all legal...whereas if i changed my plate and panels over...id have one illegal bike...one useless frame, and one good engine :rofl:

 

just change the plates over, its illigal but i wouldnt be too arsed if you dont plan on selling it

 

just change plates. i was in a similar situation and told the dvla hu decided 2 Q plate it rendering it pretty worthless