You have to rebuild the cabinet.

I meant to hold the range top not hood

Found a pic taken during installation of my kitchen. You can plainly see the shelf for the rangetop on the far right. Hope this answers your question. 😊

Looks like I should be able to just install a regular shelf

No, a "regular shelf" won't do it. It has to be dogged into the cabinet frame properly to support the weight. That is difficult to do after the fact when you don't have room to use a domino. Plus, the math has to work, and if a any part of the shelf is exposed, it has to be finished to match the cabinets. You should only need to remove the top drawer of the base though, but you will need to scoop out most of the guts surrounding the drawer for the rangetop portion to fit. That means extra support is needed.

Have you looked at the installation instructions for your product? Different models are supported in different ways. For example, these Cafe gas cooktops are supported by the countertop, not by a shelf, though you can add a false bottom. In contrast this Fulgor Milano induction cooktop is supported by a full shelf (with proper cutouts for electrical) or a shelf 2" only wide all around. Jenn-Air cooktops are different still.

FYI: "cooktop" = "rangetop" in this comment.

@wdccruise those are all rangetops you linked, but you called them cooktops. The links are helpful, but people may not click on them if they are looking for rangetop instruction and think you are linking cooktop instruction.

Edit: thanks for your edit that clarified.

Some folks just don’t understand the difference between a cooktop, and rangetop.

@darbuka: "Some folks just don’t understand the difference between a cooktop, and rangetop."

And some do. All the products discussed above were rangetops. If you search website (appliancesconnection.com, Home Depot, Best Buy) you will only find the appliance category "Cooktops". Among these three, only appliancesconnection.com includes the "rangetop" subcategory. Best Buy and Home Depot refer to all products as "cooktops".

https://ironsupports.com/products/standard-front-mount-countertop-l-bracket can I install these under a regular 3/4 shelf to support the 90lbs range top

What is the brand and model of the appliance?

Thor 36 range top

While the Installation specs do not specifically say "do not install on brackets" I'd bet if you called and asked, they'd say "no".

The range top may only be 90 lbs but there's more to it than that. Pots and pans adding weight, making sure its level, people leaning on it, stacking stuff on it, ect. It needs to sit on a solid surface.

I would think switching from cooktop to a range would be easier. Take the whole cabinet out.

As I read the USER MANUAL & INSTALLATION GUIDE, the Thor HRT3618U's four feet are to sit on a shelf (page 16) in a cutout whose dimensions are shown on page 14. The cutout is 7.3" deep to allow the cooktop surface (excluding the grates; page 12) to be even with the countertops on either side. Of course, there are other requirements and you must allow for the gas line and electrical cables to pass through the shelf to the bottom of the cooktop.

I was planning to put a shelf on top of the brackets and stove on top of the shelf.

Pick something other than Thor.

Stick with a cooktop if you want versatility and to not have to replace things down the road. Especially since you are interested in Thor, which has truly horrible reviews.

On the Home Depot website it has 4.7 stars or are those fake? What versatility does the cook top offer? Thor range is only $999. If it lasts a few years I’ll be satisfied versus paying $4000 for the other brands

@HU-791729054: "Especially since you are interested in Thor, which has truly horrible reviews."

There are 85 owner reviews on Home Depot and 91% recommend the appliance.

"I was planning to put a shelf on top of the brackets and stove on top of the shelf."

1. What were you planning to attach those brackets to? I would attach cleats to the vertical panels to which the drawer runners are now attached.
2. Remove the top drawer. Measure the distance between the vertical panels that support the drawer runners. What is that distance? It must be at least 36" or you won't be able to fit the Thor HRT3618U in the space.
3. What is the distance between the top of the countertop and the bottom of the top drawer's cutout?
4. What is the countertop material? You are going to have to cut it twice -- and leave finished edges that will abut the cooktop -- to leave a 36"-wide opening for the cooktop. Are you prepared to do that?
5. Have you considered the Thor TGC3601 cooktop instead? It's only $700 and would be much easier to install.