Yes, this is always the risk buying used engines.
RF & R2 have a different stroke length so use different rods and crank.
Its hard for me to add that edit now, but the photo showing the R2 from the alternator side, you can see the thermostat housing poking out in front of the timing cover.
Later models it is near #1 injector.
Whether the motor is worn or not will have less to do with its age and more how well it was treated.
You can gauge an idea of how worn a turbo is by lateral shaft play.
I know the HT10-9 works hard on these motors so will wear on high mileage models.
The blades should not touch the housing, also look for traces of oil in the compressor and exhaust housings.
The pics of mine show no oil, but it did have a lot of shaft play - still useable but worn.
You can buy rebuild kits for them, but they can be hard to find.
84 626 sedan FE SOHC turbo - Sold, no time to finish
84 626 sedan RF diesel - Sold, no time to work on it.
06 Mazda 6 MPS (Mazdaspeed) new fun car no mods yet
07 Mazda 6 MZR-CD 6sp manual - new DD