I've just done pretty much just that.I've put 9.7.1 pistons in an 18rgu block and an 18rgeu head 88270. Blocks are all the same just comp are different for each variant motor. The valve clearance was questionable. But once fitted and checked clearances were good.I have not started it yet, maybe next week. Though I will put a piggy back computer in it because off the cams used 88231 18rg, might run a bit funny without this and premium fuel to be used.