Hi,
Read the rules carefully, to be water cooled then you must be 125 cc and also the barrel has to be built from an original cast IRON barrel, and must retain some of the original casting. To make a water cooled ALLOY barrel is against the rules as these can only be AIR cooled aluminium BTW barrels.
175 racers must have air cooled only regardless of casting type.
There is some speculation as to the value of water cooling as the races we do are not particularly long, but as always it is down to your decision and thinking as to the way to go.
You should have made yourself known at Anglesey and you can always get help if you ask in the right way! we need more on the grid!!
Good luck with your build,
Alan