The seacock sizes you have quoted are the same sizes that Were originally fitted on my J&J Bav 36(2002). These I replaced with TruDesign grp valves which are a little more bulky than the bronze or DZR valves originally fitted and this on my single heads + three sleeping cabins boat lead to some unusual fitting techniques as the space within the under washbasin cabinet was limited such that some innovative thinking was needed in order to install the new valves. This involved fitting all of the internal parts together first, and finally screwing the through hull fitting through the hull, through the loosely fitted internal backing nut and into the connection on the valve. Lastly the loosely fitted internal nut was then tightened up to the inner side of the hull, and all with a few cuss words added on account of the awkwardness of the fitting operation due to the very limited space which prevented being able to fit and turn the internal parts. If yours is a B36, you will probably see what I was getting at if you fit the TrueDesign valves.
Good luck.