First no way vent free gas ever and I am surprised even available anymore . Do you need the heat or is this just for looks ? It seems to aslo be in a very odd spot so maybe some pics from further back.

Not loving the idea of ventless.

You may have your reasons........but the tile detracts, seems to compete with a lovely surround and from what COULD be a nice wood burning fire.

An insert was recommended by a reputable fireplace shop.

Have you shopped around? Perhaps there is more available besides what this one shop recommends? Google direct vent gas fireplace insert and you will see plenty more that don't have the large black surround. Some of them you can select the liner - brick, herringbone, black.

I don't find the stone tiles particularly pleasing nor do they seem very 1935. Could they have been added later? Would you be interested in removing the stone tile, opening up the space, and potentially enabling more options for a larger insert that looks better, and finishing the extra space with brick or something that would be pleasing to the eye?

These conversions can be very challenging. Often, the fireboxes of old were shallow, or there will be some configuration making it impossible.

We've the most "conditioned"interiors of any country on the planet.......and we're the most fire obsessed for nothing more than the look.

Clean the chimney, make sure flu etc all good, paint the interior black , and change the busy busy surrounding tile to a honed marble, or granite, or soapstone. Get logs......and enjoy the real deal.

Yes, it will take some heat up the chimney, but. You'll have the crackle : )

You said you are trying to install a working set of gas logs, yet you are showing an insert. Which is it that you want?

Here are some great looking Aspen Gas Logsand a nice Antique Brass Fireplace Screen.

Mockup by: Fireplace Treatments