I regret that I personally have no information on your father. I have found very limited references to 143 Special Service Company on these two websites:
and in the Kohima Museum website here:
The former has this as additional information:
On arrival at Kohima on 19 April, this battalion was placed under command of the 5th Infantry Brigade in lieu of the Dorsets who were then serving with the 6th Infantry Brigade. It returned to its parent brigade on 5 June 1944.
There were several different units that attended courses at Achnacarry as can be seen here: