Those units
Are T K Monotubes, 3 wire I would bet,Frigidaire units are similar, but have different bowls and supports, you CAN replace these as was done with the one with Chromalox 3 wire units. TK stands for Tuttle and Kift, these units were used on many ranges in the late 40s and 50s, Thermador, Philco and Admiral to name a few.