You have a few options. Dacor has a 46" gas cooktop. Miele has a 42" gas cooktops scroll to the bottom of the page.

Personally, I would use this opportunity to move the cooktop from the island to a more user friendly location. Is there a hood over that cooktop? Going to an island cooktop that is more powerful, I would want a hood. Island hoods are notoriously more expensive. Downdrafts are also not recommended for gas cooktops because they disrupt the gas flames. You could also look at combi cooktops, which are available through Miele, Wolf and Gaggenau. These allow you to construct a variety of cooking surfaces, electric, induction, gas, etc in 12" or 15" modules. Three 15" modules from Miele would fit the space you have. This approach allows you to have several cooking surfaces. This is an expensive option and you still need a hood. Technically, the combi is what you have from Jennair with downdrafts separating the modules.

If I were in your shoes, here is what I would do: I would move the cooktop and get a standard 30" or 36" cooktop. Get a hood and insert a wooden butcher block in the space created by the removing the cooktop.

I know it was not the question you asked but the clearances around that cooktop in what looks like an island is not ideal and unsafe if you have small children running around the house.

Good luck!

It appears you have a set of GE/Hotpoint double wall ovens, arguably one of the best baking and best self-cleaning-upper oven I assume- ovens ever, keeping those at least for the time being would help extend your cooktop venting budget.

I will have to ponder moving the cooktop idea. Right now leaning towards keeping it on island and possibly adding a hood over it. Not too keen on idea of having a big vent in middle of kitchen, but might be what needs to happen as I've been reading more and more downdrafts suck. The Dacor cooktop looks like a good option. Came across this Jenn-Air 46" gas cooktop, but was wanting more of a stainless steel look. How bad are downdrafts really? This would at least keep us from having to put in a hood.

Not sure what brand the ovens are at the moment. Will have to check to see, but they are in working condition so keeping them for a while might not be out of the question.

A search here on "downdraft" may provide a wider set of opinions and solutions, but in my view it is difficult for the air flow that is feasible (at tolerable noise levels) to divert the rising and expanding cooking plume effluent toward a downdraft intake. The rising effluent velocity can be over three feet/second. This means that the downdraft induced air at the front of the cooktop (or at least where one is cooking with a hot pan) has to be greater than that value such that the air is deflected toward the back and, as it gets closer to the back, sees an ever higher air velocity. Downdraft operation is improved if the downdraft is tall because the effluent path only needs to be bent.

It is the nature of air intake apertures that the velocity of the air rapidly drops away from the aperture, making down draft systems ineffective for front burners or very hot back burners. Normal overhead hoods operate by capturing the rising effluent within their entrance aperture and then ensuring by sufficient flow rate that momentum reflection does not cause effluent escape (failed containment).

Another effect reported for downdraft operation is gas flame deflection, potentially affecting cooking performance. This won't be an issue with induction, although the breeze across pots and pans will in both cases decrease vessel side temperature.

kas

That's a gut renovation. Trying to Bandaid it by selecting an appliance that will ''work'' is head in the sand denial about how bad that layout is, and how many changes would actually need to be made to even put in modern appliances into those vintage cabinets.