Turbo, RTV, Block off plates, and advice...

[classicauto]

The RTV should seal fine if its applied properly and the surfaces aren't warped.

Hard to say what that issue is...

As far as rebuilding before strapping the turbo on - ABSOLUTELY. And unless your engine has been rebuilt fairly recently, you'll probably need more items then a soft seal kit as there will likely be 3 piece apex seals in it. Make sure to spec out all the hard parts....but a coolant o-ring, plus all dowel oring kits from mazdatrix are only a couple hundred dollars. But oil control rings/seals, all springs etc should be measured and replaced if necessary. But in my experience, unless its been fairly recently built or freshened - you'll be in for more then you think.