3 speed vs 4 speed spline count

Hi Guys
looking to do a 4 speed conversion on a 65 dart It currently has a 3 speed on the column is the spline count on the 3 speed 23 also or will I have to change the clutch also will the 4 speed bolt up to the 3 speed bellhousing Car is a 273 2bbl.
Thanks

The spline count will be the same (23 spline).

I'm 99% sure the 3-speed bellhousing will not match the 4-speed's (I'm assuming an A-833 here) bolt pattern. You'll need a SB 4-speed BH.

Check to see if the bellhousing has 2 bolt patterns. I know the 70's bellhousings would work with either 3 or 4 speed

Same spline count, same bell housing

Same spline count, but the '66 Valiant 3-speed column shift trans that I have won't bolt up to the 4-speed '66 833 bell housings I have. It probably will bolt to the later dual pattern bell housing with the 3-speed bolt pattern.
The only reason I have that trans is to pirate the screws out of it.

In or around those years of 273's I've seen a castiron bell with a 3 speed bolt patern with a smaller 10" cltuth.

I should have added...."For 70 and up 3 speeds"