The main difference between the 2 I believe is that the Turbo350 only has 3 gears 3rd being 1:1. Where as the 700R4 has an over drive 4th gear as the name suggests. the 700R4 should be the best option since getting a strong enough Diff that is lower geared than 3.544:1 is quite expensive. Where 3.5s are a dime a dozen. Most mucle cars use 2.5-3.27:1 gears in the back. I am not sure about the other physical differences between the 2. However, a 3.5 diff with an overdrive trans should run about 2500rpm at 60mph instead of 3000+ for the 3 speed 1:.
A note about all early overdrive automatics. A commonly over looked instruction (Usually in the owners manual that nobody ever reads) by owners was to not drive with the trans in the overdrive position in town. If left in the overdrive position in town, the trans will not only shift into 4th while going 25-30mph but lock the locking torque converter as well. Needless to say this all results in burnt up transmission. Lots of 80's vehicles got bad reputations for their transmissions because of this. A good example that applies to this trans are the GM pichup trucks that people used to haul their RV's had a little trans BBQ as they went up a slight grade going 25 in overdrive OUCH!. It probably only took about 2 or 3 of these before the trans was completely hammered. Anyway, I'm obviously recomending the 7000R4. Hope that makes your decision a little easier. Ross
