110 double cab conversion

Hello guys i am new to this site and looking for some expert advice.

I am starting a build conversion from a 110 hicap pickup to a 110 double cab. As i understand the roof will be either cut and joined or a replacement sourced depending on the availabity at the time.

I am asking is it possible to just move the rear window bulkhead back and use a tub off of a 90?
Obviously if i buy all of the necessary panels...?

Or is it easier to just buy a complete 110 double cab pickup and swap everything? Then sell the donor.

The 110 hicap i have is LHD and that is the reason i dont just buy another double cab.....as they are stupid money.

Excuse my inexperience on defender part numbers and compatibility thats why i have posted this thread. For the wealth of information and experience that is on here.
Looking forward to the replies.

I don't think that a 90 rear tub will fit on a 110 Double Cab, as the roof sides of the load area are the same size as the old 88" Series 2/3 sides. Assuming that this is correct than the 90 tub will be 41/2" too long. (A 90 is actually 921/2") If parts availability is an issue, you could probably shorten a 90 tub, but the extra 41/2" is in front of the wheels.