"Are they the same motors except one is stroked and PFI instead of TBI?" Yes and no. There are differences in the crank, rods and pistons. The heads are also different. The motors are the same family and same construction and such but there are detail differences in the specific parts between the years.
All years of 4.5? I though the 90 4.5 and the 89 4.5 were significantly different.
You are correct... See corrections in edited post above. The oil pump will interchange which is what the main question was.
The 89 4.5 was a TBI engine.
The 90 4.5 was the same bore and stroke but the 90 was PFI and had a light weight piston/rod assembly and as a result the crank was balanced differently. The 90 cylinder heads had very different intake ports compared to the ports on the 89. With the PFI, the intake manifold was quite different. The oil pump will interchange , though.
From the posters question he mentioned the 4.5 and 4.9 and PFI so I was answering in respect to comparing a 90 4.5 to a 91-95 4.9 only. Should have been more specific.