While marking out the cabs I also had to take into account the width of the top part compared to the bottom one once the 2" sectioned was cut out. The taper at the A pillar showed I had to add 3 mm, 1/8", each side but the B pillar it was 6 mm, 1/4".
The back wall will mostly come from the 48 cab. It was cut as wide as possible on the lower section to just where the recessed part starts to curve. I will use the corners on the lower part from the 58 and they will be cut further along to make up the extra width that I am after. It will be more than the 220 mm that I am widening the cab because I am also making the cab longer. Due to the trapezoid shape, when viewed from above, means any extra length also makes the rear wall wider. An extra 35 mm, or nearly 1.5" wider. The upper part of the rear wall will be used completely as is in much better condition than the 58. It will be cut in half and a new piece made for the middle making the window wider. I did most of my cutting using a jigsaw and a reciprocating saw.
The top is all off and using all of it except the small centre piece left. The panels in the foreground from the lower section wont be used except for replacing any damaged sections in the other cab.
Time to start on the 58 cab. This piece cut out had a lot to take into account. Not only the extra over all cabin width of 220 mm, but also the 35 mm extra due the the taper of the cab floor from making the cab longer. Then 12 mm total due to the taper in the walls after sectioning out the 50 mm, and then also another 3 mm for the thickness of the blade when I cut the rear upper wall through the middle of the window! So 270 mm extra in the upper rear wall in the end. I don't expect anyone to follow that rambling.
The the 58 is mainly all the lower sections due to being in better condition. Would have been nice to be able to use opposite corners from both cabs cut longer to make up the extra width and length, but it was better to go with the best pieces from each instead. The small pile shown in the last shot is all the pieces that will make up the new cab.