727 to replace a 904

I agree with the others that rebuilding the 904 would be more cost effective and practical. As with any transmission, try to find someone reputable and that perhaps has some performance related experience. It's easy to build a little more durability into a 904, not that you need it for a stock 318. (i.e.: A mild shift kit to firm up the shifts.) Or look at it this way, you'll get better fuel mileage with 904 because it takes less power to turn! A new converter would probably be a good idea either way so do some research for a quality replacement. The right choice may help mileage a bit too!