"drop in" small block

That a999 trans is basically a 904 with a lower (2.76:1 vs 2.45:1) 1st gear raito also known as the 'wide' raito 904. It also has a mechanical lock up torque converter. That lock up will eliminate any slip in the torque converter when it comes on. The even cheaper route is you can swap the planetary gears in your current 904 for the lower 2.67:1 gearset & go. But no lock up converter. It makes a diffrence on take off for sure!