Starting and gearchange

[Dippydog]

Whether or not these two issues are related I don't know although I don't see how,but any ideas/pointers greatly appreciated.The car is a Y reg C70 2.4 lpt manual petrol.
Starting: When trying to start the car it will very rarely start straight away but most of the time it turns over for a long time during which the rev counter will flick/bounce up to indicating anything up to 2000 revs before instantly dropping back to zero then repeating.I tried taking out the crank sensor and cleaning the end which appeared to cure it but only for three or four starts then it went back to awkward starting.So a new[cheap aftermarket]sensor was bought/installed just to try and prove sensor fault one way or the other which again "cured" the issue for three or four starts then back to awkward starting.Bit the bullet and bought a new Denso sensor and installed that but the issue remains.I can't see all three sensors being faulty.When the car eventually does start the tickover is smooth and steady and it revs cleanly with no hesitation throughout the rev range.
The gear change is very obstructive with gears[particularly first and reverse]being awkward to engage.I must say at this point the gear box is a second hand unit from an earlier car[I understand it's from an 850 but could be wrong on that]It could be that the concentric slave cylinder has not been fully bled and I'm going to give that a try soon,other than that are the gear change cable adjustable and if so where or have we bought a dodgy used 'box? Any ideas on either or both these issues greatly appreciated as we're trying to make this car the car it should be after it's been very poorly treated by previous owners. Sorry for long post.