This is my Chop, not perfect, but here are my thoughts on the subject. I had various chats and advise from Mark (BlackPopRacing) and this is what I came up with
Bracing, probably could have been better, but it did the job, just over do it, once its moved getting it straight again would not be easy.
So, the rule is simple, check twice, cut once... Having looked at it for a while I determined the cutting points by
a) keeping the cut ends as near tangential as possible, for a smooth joint
b) Look at it from all angles to determine the tangential points
c) If you look at the back post, your see I played with the cut lines to get tangential ends
d) Think about all cuts and how they will fit together
e) Draw on the body and check and change till happy
f) Then double check all the cut lines again and visualize the final joint
Its easier changing marker lines then having to hack the metal around later
I went for a 2.5" chop and 1.25" rear window chop, just to add to the fun
As you can see, I cut the back and stitched that back together before cutting the roof top, this allowed it to sit on the 'B' posts
Picking the straightest tangential points for the top roof cuts, the front one I cut very close to the original joint, that complicated the welding back together because of the lead, so maybe it would have been better to be just a little bit away for the joints
I then cut a Classic mini roof in to finish the job, yet to be welded in, as access vi the top is useful.