I, too, use the mocal sandwich take-off plate with built in thermostat - works fine, no bleed until
oil is close to temp, but....
I had to do a fair bit of work on that thing to remove obstructions to the flow of
oil. In particular I removed metal from the area where the take-off threads run into the body - this was seriously restricted as supplied.
Also worked around and opened up the area where the themostat "valve" works - this again gave only a tiny opening for the
oil to flow through when the 'stat was wide open. You have to sit and look at the thing for a while to get the sense of where the oil is flowing under different temperature conditions to do this properly, and ensure you do not remove metal where it could affect the operation of the 'stat.
I view the "waxstat" itself as a renewable item - it definitely works less well with age for some reason. (maybe I cooked mine on the track one day - oil got plenty hot when the "red mist" came up!!)
I would take the same approach with the OT-2 oil 'stat - look at the oil passages and work on them a touch before using it. You can do without additional restrictions in the oil path in the cooler run anyway. Lastly, I would recommend -12 lines and fittings, again to reduce flow restriction - that is 3/4" ID lines.
Oh, and of course, if you take a die grinder to any part of your oiling system - clean, clean, and clean again before use. Sorry if this is teaching folks to suck eggs, but I saw a perfectly fine 410 BB ruined by honing grit once (no, it was not mine).
HTH
WIlf