Tim,
I don't know how you get the impression that the Typhoon only requires "relatively minor" mods to be a carrier aircraft. It would need a massively uprated (and preferably functional.....) undercarriage, a substantially beefed up fuselage with arrestor gear, a marinisation programme to replace/upgrade potentially corrosive systems as well as a probable re-write of some fairly meaty flight control software. Apart from the latter (which is just very expensive and time consuming...) all of the others have a substantial impact upon weight and thus performance. If you were to marinize the Typhoon you would cause a significant reduction in the platforms capabilities, eroding any margin it has over F18E/F or Rafale. Therefore, t'baron's coffers aside, there is no point in going down that route. Better to keep F-35B, migrate to F-35C (though it's not without issues itself...) or dumb-down to the super-bug. Sell T1/T2 Typhoons to pay for them if required. Remember, History is prologue. As Engines tells you there have been very few cases of a land combat aircraft sucessfully becoming a carrier one. BAES may well have some glossy brochures, snazzy powerpoints and Jedi mind tricks to seduce weak-minded lobbyists, journos and politicians - listen to the coal face, it is not worth adapting Typhoon.
USMC need F-35B for their LPH/LPDs - they cannot operate Cat n Trap F-35Cs off them. In USMC doctrine the F-35 is there to support the RW/V-22 community, therefore they co-locate. If F-35B goes, the USMC will be reliant on F-35Cs on USN CVNs -and that is not a place they want to be (think Guadalcanal....).