The 1/144 Revell 212 is pretty small, and if you haven't done this sort of thing before or have adult sized hands, may proove a little difficult. Larger modern subs at 1/144 scale include the Trumpeter Kilo and larger still, the Trumpeter Seawolf are better conversion candidates. You can purchase ready made model specific dive modules for these from Caswell as well as fitting kits which come with resin controll surfaces and plane linkages. Though by the time you've bought all this, your not far off the price of the fibreglassed T boat you were interested in, which would be the superior model in everyway. Building your own WTC and ballast system brings the price down a lot though.