Ok, that was my next question. So notch is better.
Any particular manufacture?
What are you going to be using the disk for? Before plowing, after plowing, or both? What will you be planting? Notched is better for breaking into hard ground but the blades will last nowhere near as long. I have changed both of my 3-pt disks to plain blades and they work fine, especially on plowed ground. Another option is to have notched on the front and plain on the rear. Another choice you will be seeing is either 7.5" or 9" spacing. If you are preparing a seedbed you want the 7.5" spacing especially on the rear.
I use a 10ft Ford 3-pt disk on my New Holland TD75 and it pulls and lifts it fine. The disk has 32 18-inch blades, but it is not a super heavy disk; it does the job for me. I also have a smaller MF lift-up disk with 24 blades that can be used on smaller tractors.
A new disk harrow will be expensive, maybe keep your eyes open for a good used one, keeping in mind the repair costs for worn out blades, bearings etc. If you buy a new disk you will probably want to spring for scrapers also.
If you're looking looking at new some brands to consider are Land Pride
Land Pride Disc Harrows , Taylorway-Pittsburg Hay King
K&M Mfg. Product 5 and Monroe
Well Built, Performance Driven - Monroe Tufline . There is always John Deere Frontier stuff and even Norhtern Tool has some heavier 3-pt disks. So far I've only purchased used, it's pretty easy to look at a disk and tell if it's been bent up, welded up, abused etc. Some of the older disks are better for finish work because they tend to have the narrow blade spacings and the frames have more flex or float for the rear gangs. I think one of the Monroe-Tuffline units has rear gangs that float.
As far as your plow, if you have to change the tractor wheel spacing you might as well change both sides as long as the new spacing is compatable with whatever other work you'll be doing.