550’s are OK, however, to get OD, the third gear position is removed, so shifting skips that ratio which limits on to second gear if one has a load. Short GM input shafts are not available, however GM used a special bell housing that takes the long input shaft and 14” clutch, I have one if anyone needs the casting number.
If one finds an early 4500, it will come with stock GM bolt pattern and right length input shaft, or use Dodge input shaft and 1” thick adapter plate as member just above did.
Ed
The early NV4500's do not bolt up to older bellhousings. You would have to drill and tap the case to make either the early or late case work with an older bellhousing. GM made aluminum bellhousings that will bolt to the early ('93-'95) nv4500's, and they made aluminum bellhousings that will bolt to the later cases ('96-'07).
NP540's were used in stock GM applications with GM bellhousings. The two I have have the short GM input shaft and bolt up to the same cast iron bellhousing that an sm420 will bolt up to.
You are correct that the issue with the OD versions of these transmissions are that the 3-4 gap becomes very large.
