8&3/4 axle fitment problem

Rapid Robert said
I did shine a light in & I can see what appears to be a solid round area with maybe a small hole in the center. thank you for your time

You described the thrust block exactly.

If you have taper bearings you must have it.

If you have green bearings you don't need it but it should not interfere.

Are the brake backing plates on?

Measure the axles and post here.

Press the bearing retainer toward the spline end and measure from the inside of the retainer to the end of the splines