For what you are going to spend doing the trans swap you could probably afford to go through 3 UN-1 boxes. Unless you are tracking the car it probably isn't worth it and if you ARE tracking the car you must consider it disposable (the whole car) because if you are driving that close to the car's limits you are going to bend the car eventually. For all but the most extreme driving the UN1 with the Holloway upgrade and the Quaiffe diff is more than enough. A lot depends on how you treat it. Shock loads will quickly rip the teeth off the crown wheel and damage the gears. The UN1 was not made for drag races and "dumping" the clutch. Other than that it can last a long time. Upgrading the tranny only leads to upping the HP on the motor. Then it's the brakes. Then it's the cooling. On and on. Where do you stop? If the Lotus is not enough car for you maybe a better swap is to get another car. Before you start going down a very expensive road you should know where you intend to wind up. Do not discount resale value of your modified car. Even though you will put a LOT of expensive parts into it you may actually DECREASE the value of the car! Especially after you start flogging it!