The only problem with the T800 was that Boeing signed an exclusivity deal with GE.
I can't remember what the time is from start to finish of an engine is now, but probably about a week/ten days. There will have been no redundant parts in the sense that you mean, they would just have become spares for the few that were sold.
It will probably come to nought but there was a rumour about re-engining the Antanov with T800s
You may be thinking of the RB211, which Trent engines are all iterations of, and which caused the bankruptcy of RR. That was meant to have composite fan blades, which have only in the past very few years became a manufacturing fact, so the RB211 was about 40-50 years too early.
The major problem with composite fan blades is what should not happen after bird strike or foreign body ingestion...... That has only just been mastered, first by GE, now by RR.