engine swap

I have a 89 bronco with the 2.9L. Its 4 wheel drive. I had to replace one of the heads and since i have there is gas going into the oil. I assume the only way its getting in is through the intake but i took it back apart and couldnt see anything. but anyway, i was wondering correct me if i'm wrong but a 4.0 is interchangable with the 2.9 right? ok and if it is will it fit?