Regarding length over Scottish course? Excellent for run (5,4)

I believe the answer is:

relay-race

'run' is the definition.
(thesaurus)

'regarding length over scottish course? excellent' is the subsidiary indication.
'regarding' becomes 're'.
'length' becomes 'l'.
'over' means one lot of letters go next to another.
'scottish course?' becomes 'ayr' (Ayr Racecourse).
'excellent' becomes 'ace' (I've seen this in other clues).
're'+'l'+'ayr'+'ace'='relayrace'

'for' is the link.

I've seen this clue in The Times.

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