artful: I just completed my searches of Rutherford's books, and a couple more timelines of the doctrine become apparent.
By 1932, they seem to have moved away from the "spirit conversion" theory:
Vindication III (1932) pp. 296-7 (bold added):
The east inner gate will be open on state occasions: Now when the prince shall prepare a voluntary burnt offering or peace offerings voluntarily unto the Lord, one shall then open him the gate that looketh toward the east, and he shall prepare his burnt offering and his peace offerings as he did on the sabbath day; then he shall go forth; and after his going forth one shall shut the gate. ([Ezek] 46: 12) This is a further testimony of the loving-kindness of Jehovah, showing his consideration for the faithful prophets of old and that they will be favored with a better resurrection." There will be nothing about their service that is compulsory, but they will serve joyfully, willingly and with a ready mind. They will be happy to worship and make offerings of praise and thanksgiving to the Lord privately and when not acting in an official capacity with the people. Note that when the princes conclude offering their voluntary (or free-will) offering he shall go forth; and after he goeth forth one shall shut the gate. This shows that the doors of audience with Jehovahs heavenly priesthood will always be ready to open to these princes of the earth whenever their personal needs require them to seek communion with the Lord of heaven. And it shall come to pass, that before they call, I will answer: and while they are yet speaking, I will hear.-Isa. 65: 24.
By 1941 they had abandoned the "eventually gonna be spirit beings" theory:
Children (1941) pp. 178-9:
Faithful men of old, from Abel to the last one of the prophets, cannot have a part in the first resurrection, for the reason that they died before the heavenly way was opened and before anyone was called to the heavenly kingdom. The life of those faithful men shall be forever human on the earth.
But they still held that these men would be resurrected as perfect humans:
Children (1941) pp. 181-2:
Their resurrection shall take place, according to the Scriptures, when the Kingdom comes and begins to function. When raised from the dead and given life they will be the children of Christ Jesus because receiving life by and through him. Therefore it is certain that those faithful men will be raised from the dead as perfect human creatures, and be appointed to and occupy the high position of princes [or visible overlords or sovereign rulers] in all the earth. They will not be a part of the Holy City, or THEOCRATIC GOV ERNMENT, because that is spiritual; but they will occupy the high position of visible representatives of the Holy City, or THEOCRACY, and will govern or rule the peoples of the earth...
More to come?