Which trans is better for racing short tail shaft 727 or long tail shaft

Pretty much..... the short tailshaft is better for vans and trucks because that is what it was designed for and bolts into. Likewise the long tailshaft is better for cars, same reasons.

The internal workings are the same. Most shorties have heavy duty internals as they are truck transmissions.

If you dont know, the long shaft transmissions use a slip yoke output which is simple to use in a car. All cars used slip yokes. The shorties had a fixed yoke and are designed to use with a hanger bearing and 2 piece driveshaft.

I dont believe that, other than one bad hack job conversion, I have ever seen a shortie in a car.