Spindle OD can be assessed using “V” blocks and a known flat surface (surface plate or machine table).
And a good tenth’s reading indicator with surface gauge or height gauge.
Testing the contact of a good spindle to the bushing is done less thrust washer using Prussian blue.
For the professionals only. Back then when the FP1 was introduced MT was universal for a toolroom machine which doesn't need rapid tool changes. MT4 tooling is available at reasonable prices and for a beginner hobbyst it would be just fine.
Maybe you can find one in EU and have it shipped to a reputable member here for inspection and re-shipping.