greetings from Texas salbwil,
personally I would not recoment a woodburning insert into the old heatilator UNLESS, what you are calling a heatilator is actually the old masonry insert which is just a steel plate three sided box with 2 blowers mounted (usually in the hearth that push out air in slits in the brick over the fireplace. If thats the case the fireplace is called a heat form and its perfectly fine to install an insert into. and really not that big of a deal in the install. If the fireplace is truely a zero clearance unit called a heatilator I would recomend updating to a newer unit. And if you are looking for an actuall heating unit I would recomend looking at EPA certified fireplaces or even a free standing wood stove in its place, without seeing the situation first hand its hard to tell you a true direction in which to go. If you would like to email some pics I would be glad to look at them and then make recomendations as to what I would do if I were you.

Hi rick,
Fireplace sounds like the first one you described with " soldier course" across top line of bricks and fans installed . The fireplace is the widest they made at the time ....4' opening. The man that built and installed the fireplace has since lost his license in our city as a few of those he did had wall fires, so I cannot use the same mason.
Thanks for your help,
Salbwil