Very nice!
"J" line of ranges would be 1965. Frigidaire started the changeover to letter designation for model year with cooking first, laundry changed over with the "K" line, 1966. Several revisions of these happened by this model - most apparent is the control arrangement, clock and the pattern on the oven door glass. I would be surprised if the Heat Minder burner doesn't work, depending on the type it is. Does this have a "Speed Heat" burner on the left front? Most likely, that is where a problem will be with Frigidaire burners, the switches were trouble-prone.
A few weeks ago, there were two 30" Flairs in the same house, one in the basement. One was white, the other coppertone, both with the base cabinets attached. They were asking $200 each for them, I got them down to $35 the last day of the sale and then decided to let it go, I have no room for more!!