Distributor question

[87GT Drop Top]

My friend just picked up an 89 5.0. It's doesn't have a distributor. When I look up one at work it shows 2 different ones. A cast iron gear or a steel gear. My computer @ work says they are not interchangeable. If that's the case why does the after market only show 1 part #. My guess is they are interchangeable. Does anyone know for sure?
Thanks

 

[CDQICKGT]

If you are running a oem style cam you need the steel geared on.

 

[WHT306]

If you are running a oem style cam you need the steel geared on.

+1

 

[87GT Drop Top]

Thanks going to roll with it.