I well remember the 600 Montjuics in the late 70's early 80's, I was racing a standard bike at the time, I do seem to remember that the 1000 cylinder liner was used, albeit much altered from stock, and that Jota pistons were also used, again, with many modifications to the crowns to suit the four valve configuration, in the end, kits were available, could the pistons for those kits have been Omega ?? I cant remember who made the liners but someone in UK did.
CLEM