For difficult access, nothing beats the  Lutron DT1236L laser tachometer. This unit also measures linear speeds & contact RPM measurement. The non contact measurement can be made with reflective tape on the shaft, or white paint for close range. Contact measurements use a rubber cone [shaft centre drilling] or rubber rimmed wheels for linear speed.

These components are replaceable separately.

For fixed installations Lutron makes a panel mount 48x96 digital indicator for inductive or optical pickups.

High Performance Low Cost type K Digital thermometers with and without data logging to 4 channels