I've fitted a Westy roof to a non-sunroof bus before. I bought the roof off 
a crashed westy and cut out the sunroof section with a huge disc cutter 
(great fun). I cut a hole in the bus's roof (its easy) and gradually 
enlarged it so that the sunroof section would sit inside. The sunroof 
section was trimmed until it overlapped the roof by a couple of inches all 
round. To avoid cutting through one of the cross members in the roof, I cut 
and shut the sunroof section by about 6 inches, then spot welded it all 
round. The original roof is double skinned so I made some plates that were 
riveted between the sunroof surround and the rail around the roof to stiffen 
things up. Once the headliner is in and the pop-top is on, you can't see the 
joins. When you remove the pop-top, make accurate measurements of the 
mounting holes and get the plates that are riveted inside the roof, under 
the hinges. If I was to do it again I wouldn't bother using the sunroof 
section and just stiffen up the edges of the hole with some tubing. This is 
the way all the other pop-top conversions are done, only the westy uses the 
sunroof as a basis. As long as you leave both the cross members in the roof 
it is solid enough to sit on anyway, and if you use a solid bed there is no 
problem, but if you are using the folding cot things you will need some 
strong mounting points.

Andy E.

A.C.Erskine@lut.ac.uk