87 - 93 Mustangs have an egr system (exhaust gas recirculation system) Part of it is the spacer between the throttle body and the intake. Stock is about I think 57mm (both the throttle body and egr spacer) So you need both for the 70 mm to work
If this is going on to a stock manifold you're wasting your time anyway. The stock tb opening is only 63mm. Even if you port matched it to accept the 70mm tb/spacer, the lower intake is the bottle neck and it gets all the air it wants with the stock tb/spacer setup. Hold onto that tb, pick up a used cobra intake (with the cobra you won't need an egr spacer), and put them on the car at the same time.
If this is going on to a stock manifold you're wasting your time anyway. The stock tb opening is only 63mm. Even if you port matched it to accept the 70mm tb/spacer, the lower intake is the bottle neck and it gets all the air it wants with the stock tb/spacer setup. Hold onto that tb, pick up a used cobra intake (with the cobra you won't need an egr spacer), and put them on the car at the same time.