Rear gears are probably cheaper.
I have several years experience with the od box. I didn't like Second gear much, until I installed 4.30 gears and a GVod, then used it as a splitter. Seven gears was a blast for a while but in the end, on the street, seven was about two to many, and having to split gears all the time, just got old.
With a high pressure lo-performance engine, with a broad powerband, I think it would have been ok.
There are several guys here on FABO running the od box behind 340s, and are NOT unhappy.
But IDK if I would try 3.23s. your cruise rpm is likely to be about 65=1900. While comfortable, it won't break any fuel-economy records, with a typical "bit of a cam" . The reason being, that it is impossible, with the stock-type distributor, to satisfy the engine's need for spark advance.
