That's a good shot! I regularly use my RB67 in the field with the 140 macro plus the no. 1 and 2 tubes stacked together. It is quite a heavy setup, but with a focussing rail, mirror lockup and the chimney finder surprisingly easy to use. The only downside is trying to remember which knob to loosen on the tripod/ball head/focussing rail/camera to stop the whole thing from flopping over with an alarming 'thunk'. The quality makes it worthwhile. Interestingly, the manual for the RB67 ProS states that the 127mm lens is the only one that will not have vignetting when the no. 1 and 2 tubes are stacked together, but I can't say that I've ever seen it in other lenses.