[westofb]

I agree with S nova, the overdrive will exaggerate your highway speed power loss. Your current set up should have plenty of power at road speed. To make the swap you will at a minimum the following issues: they are different in overall length, thus your driveshaft will be too long I think ( I think the 400 is shorter); the 400 tailshaft is too large for the 700, it the 700 is the same as a 350; the transmount will be different. They may be others these are the ones I thought of off top of my head. If you do the swap, you might consider a rear gear swap to a 3.73 or 4.11 to really take advantge of the overdrive by increasing your low end power, quicker lanches, etc.