An example of the traditional translation of John 4:24 into English is:
God is a Spirit: and they that worship him must worship him in spirit and in truth. (KJV)
There is not much variation in the 38 versions found here. All of them start with "God is Spirit" or "God is a Spirit" except for The Message Bible which says "God is sheer being itself - Spirit". The Message Bible is not really a translation, however, but even still all that has been added is a definition (of sorts) of Spirit and the meaning of the verse has not been altered.
The Joseph Smith Translation (published 1867) renders John 4:24 this way:
For unto such hath God promised his Spirit. And they who worship him, must worship in spirit and in truth. (JST John 4:26-2 verses added earlier in JST)
This is a dramatic shift in meaning from what God ontologically is to what God has promised.
Is there anything in any extant manuscript source that can substantiate this rendering?