You need 10mm spacers x 4 M10 fitment , and like Kike says , you can get someone to machine up a set , or you can look at ebay for sellers . Might not be able to get captive spacers easily on ebay tho , but people using plain spacers I know of are , by all reports okay using them . Reduced head race hex titanium bolts from Racebolt.uk are what I have fitted to my 14R Kwacka , and ex Busa . Braketech make a ti piston set for GP4-RX .