I have been down the track of the RB30 bottom end. I had prices from two credible workshops to supply a prepped block and crank girdle/adaptor and they ranged from $5-$7k and thats before you buy a crank, rods and pistons so I don`t see how that comes out any cheaper. It seems that a lot of workshops will tell you how cheap this conversion is untill you actually come to do it and the price doubles.
I realise that they can rev the OS Giken RB30 to 10,000rpm but I don`t think you can compare a standard RB30 block and crank to the sleeved block and high end forged crank of the OS kit. I have heard that the standard RB30 crank is forged but I doubt it matches the quality of the OS crank.
If anyone can do the RB30 conversion for a guaranteed price and quality I would be more than happy to talk to them. I just hate getting nasty surprises when it comes time to fork out the dollars.
Cheers, Dror