What proof can you provide to validate the OS Giken bottom end?
Is it an OS RB30 or RB315?
Can you provide a full list of modifications?
OS Giken does not make 'blocks', they sell complete assembled bottom ends built to withstand up to 1400HP, which consist of an RB26 block, OS Giken spacer plate and liners, OS Giken forged crank, rods, pistons and more.
Take some photos of the engine and the spacer plate between the block and the head should be very obvious, this will substansiate if the car is actually running an 'OS Giken RB30' or just a run of the mill RB30, or something else again.
Thanks.