If you are keen to change both the rear and the trans, then I suggest a change to 3.23s to go with the O/D box. This gets you a 9.98 starter gear, and a 2.32 highway gear for 2100ish cruising.The 1-2 split at 54 % is still a bit annoying but its liveable.The reduction in cruise rpm of about 22% should net about 2 mpg. The 2.94s would work also, but the large 1-2 split means the engine will have to work harder from the 10% higher roadspeed. It seems better to short shift the 3.23s, than to run the Rs up higher with the 2.94s. This thinking harks back to the 3.55s that you already have. Given the options, I wonder if the trans swap couldnt be first on the list. Then just learn to short-shift second. The ratios between the A-230 and the O/D box are very similar, and that box is often found cheap.It will take anything your 360 can dish out. Just remember the O/D gear is strictly for cruising.No speed shifts into it.You dont have to treat it like glass. Just be nice to it.

Hope you got my reply. Im still struggling with this system