Since I think its pertinent here, and I'm curious, can you share the details of your front end swap? It looks like you used the earlier (Pre 95?)DR650, which from what I've found, should be pretty straight forward.
Actually it was a 2003 front end, and in great nick too. Late DR650s are not so common on the UK. We did the same as you: shortened and turned down the stem so the DR triple clamps and bearings fitted onto the GS headstock. To others: try and get a complete front end with wheel, disc, caliper and so on. Little bits like the speedo drive cost a fortune (could not find used, even on US ebay).
I cant recall if we knew a DR650 swingarm would slot in, and if we did why we didn't do it. We've certainly talked about lengthening the GS swingarm (steel), but right now it looks like the 19" will fit.
I dont know the exact shock space complications, but if you have a ready-assembled DR back end with wheel and brake with just the sprocket to line up, that could be less work than lining up the DR wheel/hub/brake in the GS arm (that's being done now).
btw, I recall rattenshaw mentioning the pegs are too far back for easy standing and weighting - they are.
It could be a major ergonomic issue, and moving it all forward is not so simple - is it?