In the UK we are very good at self criticism and very open about the problems with operating our equipment, in the USA the attitude is very different with people keeping the company line and working behind the scenes to sort out any problems. I am guessing that the L1011 is not as bad as some on this forum would paint it and for this reason is not a bad investment for this work.
Other factors may well be, the parts supply chain in the USA will be good with the large amount of L1011's that have been withdrawn from service, the Americans will be much more street wise in procuring parts than the UK MoD, suppliers of services won't be able to hike the price of services like they do when it is a military contract. ( I know of one supplier to the UK MoD who adds 300% to anything supplied to the MoD).
Add to this the less restrictive operational attitude of a civil operator than the 6 covering will this decision effect my career attitude of some in the military and this L1011 operation stands a good chance of being financially viable.