So I bit the bullet and removed the 6mm spacer. Next job is balance carbs and tune. Hopefully this weekend. Got everything I need in place at last, including my next three project bikes, the two ZZRs were £400 for the pair, the GSXR was £1500. All bikes are complete, some parts are removed though, they should be delivered in a few weeks time.
1990 ZZR600
1993 ZZR600
1988(ish) GSXR400 Slingshot (Slab side) - This one's a keeper.