Of course you can get a 27-inch size range/vent hood custom made (even Imperial does that). But would you want to do that when the recommended size is quite different than the space you have available and want to use "as is".

Copied from a Lowe's "How to install a vent hood" site (my emphasis is in caps): "Check to make sure the new hood will be 24" to 30" above the surface of the range and WILL COVER AT LEAST THE ENTIRE COOKING AREA. A 3-INCH OVERHANG ON ALL SIDES IS PREFERABLE. Be sure the wiring that will connect to the hood protrudes at least 12" from the wall. Ya-da, ya-da, ya-da......"

According to recommendation above it sounds like the first/original range in your home may have been replaced with the down-draft vent model (Jennair) BECAUSE the PO didn't want to mess with getting a properly sized vent hood for a later (and then standard size) 30-inch range. At one time your house may have been outfitted with a 24" range (hence, that 27" hood over top).

Personally, I don't think you'll ever get good venting from a 27-inch vent hood over a 30-inch range.

Just how much cooking do you do? You don't HAVE TO HAVE an operational vent hood.

I rarely used my old one in 30 years and haven't used my new one (installed in April) yet. Your oven vents into the kitchen already, either out a back burner or out the front of the range.

You'll just get a bit more steam and other vapors in the kitchen proper without a hood. Heck, open a window. It wouldn't be a big-ee for me. You can get a nice setup when you do a whole kitchen reno in the future.