Probably for good reason too, unless done properly a shaft extension could come loose with a 2KG load (wobble saw)on it and cause serious damage to the machine and probably the operator.
The best course of action would be a complete new arbour which is longer than original, but having this done professionally would cost a fair bit, may be worth it on a decent saw but not so much on a Chinese hobby grade machine.
There are wide kerf blades that will fit most saws . Usually 1/4'' . Taking a few passes for wider cuts.
I have a dado stack but find unless there are a lot of same size trenches to be done on a project then the faffing around setting things up is hardly worth the effort.
Don't go near a wobble blade unless you like hospital food. I have seen them mentioned in very old woodworking books but there is fortunately nobody selling the washer sets these days.
I’m sure you’re well aware if you work in a machine shop but I must stress that you make sure that the extension is well fixed and threaded opposite to the rotation the on the tightening nut, the last thing I want to hear on the news is that someone took their face off after a wobble saw came loose during startup on account of the weight of the block not wanting to spin or after cutting force was applied which would undo a nut that was threaded the same direction as the rotation.
It’s very simple but very easy and dangerous to overlook.
Am I right in thinking you're making the extension in a machine shop but using it at home not in the shop? I think if used in a commercial shop it would be frowned upon and in the event of an accident the powers that be would come down like a ton of bricks.
Perhaps I'm wrong about that as I don't know too much about them and personally have absolutely no desire to use one, there are other ways to achieve similar results.
If the op is making a new adaptor then I would suggest that it be designed to take a full dado set. Wobble blades are a bit of a bodge and do not cut a flat bottomed dado. The wider the dado, worse the problem becomes and can lead to a weak joint.
Set up is more awkward to as the distance from the edge of the dado cannot be directly read from the fence setting.