you can assemble it both ways,,its better for spraying or painting to assemble cab first,,then push interior in,,spray or paint the roof seperate and fit it last easier to fit the windows, this way steve gerry

Howard is the specialist on building Scania cabs...however, I will give it a bit of a go.

If you glue the door panels to the insides of the doors and then try to insert the floor pan with the dashboard attached, the dash will catch on the door pockets. The way around this is to cut off the front corner of the door pockets (which can't be seen anyway), or to glue the dash into the cab before inserting the floor panel (like Danny does).

I've also seen builders who actually glue the door panels to the floor pan -- I've not tried that yet, although I did try that trick with one of Howard's update kits, and it worked fine.

When I built my McFadyens Scania I just trimmed down the door panels with the knife and glued them to the cab floor, making sure that they never stuck out any further than the floor pan, so they didnt catch when inserting into the cab from below. They sat pretty close to the cab doors when inserted, so it didnt look any different.
I think Howards R series updated interior kit is the proper door panels and are thinner anyway.