I know where you are coming from Colin, being a BSA man myself I have seen all sorts of scope off sets with various rings on BSA breaches. The mounts BSA used to supply with the Ultra were some of the worst! I have a pair of Sports match 25mm medium mounts that align near to perfect though and I have used some Richter optic mounts before that were spot on! these day I tend to use BKL as they are always central.
I have some BKL risers sitting doing nothing too but these wont solve your problem of getting your forward mount in front of the breach rail, they do however manufacture 4" long riser rails which would do the job. you would also need another riser block for the rear mount though.
HFT, for people with only 2 buttucks!
VooDoo TwoTwo The next chapter.