I have a question about your setup. How does the oil drain back into the forks?
With the fittings in the center of the tank, it looks like they would only drain out about 40% of the oil, if they were full to begin with.
I have this setup on an '01 250F and my '03, which has '04 forks. On the '01, I relocated the holes for the fittings below center, as I mentioned in the web write-up, plugging one of the original holes, and screwing a Schraeder valve into the other for pressure relief.
On the '03, I did something like what you do with yours. I soldered a piece of copper tube that is bent at a gentle 45 degrees to the inside end of each metering valve so that its end stands just of the bottom of the tank. This way, the rebound stroke removes the bulk of the oil that gathers.
The '01 has always put oil in the tank very slowly, probably because of the small size of the holes i drilled in the spacer. The '04 fork has no such part under the cap to baffle out the oil, and would ship oil upstairs a little more quickly. However, I never noticed any problems arising from having oil in the tank, even when they were installed just as shown. I attribute this to the fact that I run the oil level quite high with the tank in place, which keeps the oil above the fork's operating minimum, and since the overall air volume remains the same whether the tank is empty or 45% full (the most they could get to be), it never showed up as a problem. In any case, the most oil I ever found in them was perhaps 7cc. The tank volume is fairly large, also, at just over 8 cu/in
The forks will balance their own oil level with a single tank, as well. If one fork blows 20cc of oil out, it would have more air in it than the other fork, which would give the opposite fork a "higher compression ratio" in effect, and the next few compression strokes would blow from that fork through the tank to the side with less oil. The fork with the higher oil level would be more prone to expelling oil anyway, even if they were both open. It's always worked out that the oil pretty much stayed in the fork, and the oil level was very nearly equal in both sides.