I was at a race meeting yesterday and was chatting to a guy who had custom made his own aluminium rear shock tower for his RRR.
He used 3mm aluminium plate and used the existing shock tower as a template to cut out the new one.
From there on, he simply used his dremel to trim it to size and again used the original as a template for the holes.......needless to say it appeared to work quite well and he was rather pleased with it.......he also finished 3rd in the A main using it, so it cant be too bad
Cheers