No converted -400 (or -200 or -300) have had the nose-door installed - that's only ever been an option on the production freighters.
As for height/width restrictions, the NCD offers a height of around 254cm, whereas the SCD has a height of 310. The NCD is also quite a bit narrower, at a minimum of 264cm vs 341 for the SCD. There's also height restriction all the way from the nose to behind the 'bump, with a max of 243cm vs 300cm in the remainder of the main-deck. Since the 'bump' on a converted -400 is quite a bit longer than on a production freighter, there are an additional 2 positions affected by the restriction.