One thing that has been overlooked in this post so far. The last time I checked, the 833 and 833OD bellhousings are NOT the same. The input shaft bearing retainer on the 833 is smaller in dia than the 833OD. So if you try to put the 833OD in place of the 833 it physically won't fit the bellhousing. If you have an 833OD bellhousing an 833 will go in the hole, but not register tightly to the bellhousing; it will only locate off the 4 mounting bolts. Once upon a time I remember that someone marketed a spacer ring to put on an 833 to snugly fit the 833OD bellhousing for people wanting to put an 833 into an 833OD equipped vehicle. I don't have the manuals in front of me but I don't think the 833OD bearing retainer being turned down to fit the 833 bellhousing was a recommended option. Maybe Passon had the spacer ring? I guess you could have the hole in an 833 bellhousing enlarged, but since the bellhousing has to come off I would just keep it stock and find an 833OD bellhousing out of an Aspen or Volare to replace it. Then if you want to go back to the 833 you would still have the correct bellhousing. 833OD's are aluminum cased, and since in OD you are actually running in third through the countershaft cluster and not straight through you may want to verify that the case isn't worn where the cluster shaft mounts. Hope I got the terminology correct and that this may help someone avoid a WTF moment while lying on their back trying to wrestle an 833OD into place.
Found an aluminum cased 833OD. Using Chinese calipers (probably more accurate than I can measure ham-fistedly at poor posture position), with a rusty bearing retainer I came up with a diameter in the range of 5.13-5.15". Curious how close I came to what it's supposed to measure. I don't have an 833 to compare it to.
CoolVibes and RodgerDodger, I would think the Aspen / Volare bellhousing would fit your Dart, guessing you have a 10 1/2" clutch now. I don't know what the Brewers mod will cost, but once the hole is enlarged you can't go back unless the spacer ring is still available somewhere. It might be cheaper to change the bellhousing, too; I don't know what Brewers charges for this mod.
With the 273 guessing the small clutch bellhousing. Unless I'm confused with two folks talking the same mod to two different cars. I thought going from the small clutch to the bigger clutch was worth it, had to trim one finger off the bellhousing. I didn't have an exotic exhaust system, I guess that may pose an issue if both want to occupy the same space in an early A.
I hope this helps, CG.........................