Open pillow blocks are designed to be used with fully supported shafting.
There is a T-bar support that they make for the shaft and the shaft comes pre-drilled for bolting to the T-bar.
If you are going to use end supported rails you should use closed bearings.
Open bearings are a more sloppy fit due to lack of closure but the supported rail removes deflection, on the other hand, closed bearings are much better than open but then your shaft is flexible because it is only end mounted.
The square block linears are WAY better than round (a SR40SS perhaps) but cost more as well.