Alas, the more I look at this, and think about it, the more I think that I will probably have no alternative than to return the Tt radiator and go off-brand ;-) with one of the competitors that offer a 130mm-wide 480mm radiator.
However, again, looking at the Barrow schematics (and sample parts list) here -> http://www.barrowint.com/index.php/article/970.html I am beginning to wonder if something else that I had overlooked is going to come into play here. And that is the fact that they (Barrow) have based their layout on 14mm OD tubing, apparently not allowing for the possibility of 16mm OD tubing.
Also, upon first inspection, it looked like Barrow had simply chosen to place their outlets, on the distribution side, entirely too close to the side of the radiator. However, I just looked over their implementation again, and I realize that they were constrained by the location of the pairs of radiator-mounting-slots on the P90 itself. I see now that this split design of theirs (distribution on the left, reservoir+pump on the right) could not have been implemented in any other way... Although, I suppose they could have located the G-1/4 outlets between the plate's clamping screws and picked up another couple of millimeters of clearance.
So, as I have tried to make clear above, even acquiring 130mm-wide radiator, and implementing some kind of spacer kluge might still be insufficient to making this work with 16mm OD tubing. But, of course, as I typed that I realized that I had been making the further assumption that I would bring my tubing straight up from the distribution surface, and make the first 90° bend with the tubing instead of using 90° fittings on the plate like Barrow illustrates in their schematics.
Well... even if no one else has done one of these builds and I won't be getting any advice based upon such experience, I think that taking the time to puzzle this out and writing it down in this thread have gotten me a lot closer to a resolution on my own. Needless to say, however, I still would be very keen to hear additional ideas and alternatives.
Thanks again,
- s.west