It is 523 on this page
http://www.kingstonmouldings.com/pdvospermtb.htmI'll scan the plan and send it on if you like, you can probably buy the fittings kit from Jonathan at Deans Marine, or get the bits separately from Chris at HSL Mouldings.
I think the hull must be the Kingston one, the Deans one is not quite the same, for example the exhaust ports on the sides are moulded in. Don't bond the deck down until you get the plans, it looks to have been cut too narrow from your photos. There were two versions of this boat, the first ones saw wartime service and were numbered 379-396 (from memory), and the ones which weren't completed until hostilities ended, Nos 523-537 (I think). The difference was the first batch were true MTBs with 4 18" tubes, a twin 20mm Oerlikon machine gun up front and two twin Vickers .303 MGs aft. The later boats were supposed to be effective as MTBs and as MGBs as such had a much heavier gun armament, with a 6 PDR QF gun up front, the twin 20mm was moved aft plus the .303 MGs, but only two 18" torpedo tubes..