the converted one will be the same as the base model 229, the slide and barrel will be the same length not the slightly adjusted length of the .22 barrel and matching .22 slide. The frame and internals are all the same if you have the classic or major caliber 229, the conversion kit is just a regular 229 slide(including rod and spring) and barrel with the appropriate mag.
I still don't know why sigs pricing works out that it better to start with the classic and add a major caliber conversion, than the other way around, since you end up with all the exact same parts(base model only). But hey if you're looking at buying its a great deal