Here is a further refinement of my researches on the history of N4610.

There is a good piece from the Zimbabwe independent on the provenance of N4610 which answers some questions about inconsistencies in the database info I was looking at.

The plane impounded by government on Sunday carrying suspected mercenaries on their way to Equatorial Guinea to stage a coup has been in service under different owners since 1964, information at hand indicates. The aircraft, whose registration number in the United States was N4610, made its first flight on October 15, 1964. The ex-commercial 727-100 was formerly N4610 of National Airlines in the United States. Records show that it was previously owned by NAL (National Airlines)/PAA (Pan American Airlines). PAA bought NAL.

It also operated as ANG (Air National Guard) 4610 (c/n 18811). Its previous engine number is given as PWJT8D-7B, while the past registration number is supposed to be 83-4610. ANG is a vital part of the US Air Force. . . .

The plane was then sold by US Air Force on January 11, 2002 to Dodson International Parts, and then to Dodson Aviation on January 14, 2002. Dodson International Parts Inc, which belongs to the same group as Dodson Aviation, has a subsidiary, Dodson International Parts SA (Pty) Ltd, which is based at Wonderboom Airport in Pretoria, South Africa, from where the seized plane took off on its way to Zimbabwe.

This makes sense to me. Aero-web.org lists planes with serial numbers 83-4610, 83-4611, 83-4612, 83-4613, 83-4614, 83-4615, and  83-4617 as being C-22Bs. The site describes C-22Bs as being Boeing 727-100 "modified for air national guard support missions."

This implies that they were all custom built for the U. S. Airforce. However, I don't think this is the case. Rather, I think the planes acquired by the USAF were bought used and were customized in 1985. My mother, a retired Boeing engineer and the source of the information that the original tail number is associated with a specific set of drawings in Boeing's archives, also tells me that the plane has a relationship with Boeing throughout it's lifetime, in that Boeing provides modifications and maintainance during the life of the plane, and the drawings associated with these services also must be tracked and associated with the original tail number.

Jetlairiners.com lists dates in the early 60s as the maiden flights for 83-4610 - 83-4617, but lists a date of Halloween 1985 as Boeing's delivery date on all the C-22Bs also listed as operated by the U. S. Air Force. Putting together the history of N4610 as described in the Zimbabwe newspaper above with some of the more cryptic acronyms on the Jetairliners.com page, what I think is that National Airlines ordered the whole sequence of 727-100 model 35 planes from Boeing and took delivery in the early 60s. Then in the 80s, when Pan Am bought National and drove them into the ground, the planes were sold, and only four of them -- 83-4610, 83-4612, 83-4615, 83-4616 -- were sold to the USAF. (This in contradiction to the serial number list on Aero-web.org.) So only four of the planes on the sequence became C-22Bs.

In the comments, someone who wishes to be known as "A" points out:

I found photos of this suspect plane on airliners.net one from 2001 and the other from 1987. 83-4610.

This turns out to be a really useful link. Airliners.net is a searchable database of photos of airplanes. Searching on Boeing C-22B pulls up photos of all the planes I now think were modified to become C-22Bs and none of the rest from the sequence. (Whee! Confirmation of my new hypothesis.)

The site includes two pictures of N4610 while in use as a US military plane. Here's a nice big one of the plane in use as a US Air National Guard plane at Cottesmore (Oakham) (OKH / EGXJ) the UK on July 30, 2001 taken by photographer Robert Flinzner.

And regarding the N4610 Official Action Figure set, there's a really entertaining piece on Allafrica.com (you might have to pay to read it) from the Johannesburg Mail & Guardian: Rent-a-Coup: Who's Who

The men behind the alleged Equatorial Guinea coup plot represent a who's who of South Africa's mercenary market - but key players also have links to the American and British security establishments. ...

Mann, a former British special forces soldier who has been resident in Cape Town and who is known for his association with disbanded South African mercenary company Executive Outcomes, was earlier a senior member of Sandline International, a private military firm which has been regarded as close to the UK security establishment.

Du Toit was arrested with 14 cohorts earlier on Sunday in Equatorial Guinea. On Wednesday he "confessed" on national television that the plan had been to remove the West African country's President, Teodoro Obiang Nguema Mbasogo, from power to make way for exiled opposition leader Severo Moto Nsa. The latter has denied his involvement.

Du Toit is a director of Miltary Technical Services (MTS), a Pretoria company whose founder, Tai Minnaar, worked for the CIA in the 1970s and seems to have retained contact with the organisation until his mysterious death in 2001.