Estrata

Hello! I have a 50 year old kiln made by Knight in excellent condition - it was barely used and just stored in a basement for years. It has a NEMA 10-50 plug on it (the straight blade one). I am having an electrician come in to install the outlet (I have a double 50amp circuit from an old hot tub he will use, probably). My question is, do I have him install a an outlet for the 10-50? I've read they are not grounded and were meant to be phased out. Or should I replace the plug, and if so, what should use? Thank you!