That sounds like a possible "Plan D" (or is it Plan Z ? ) ... but I hope I don't need to go that far down the alphabetAnother weapon in my arsenal......
A length of 6mm threaded bar, heat flattened at one end and drilled to accept the spring hook.
A piece of flat steel bar spanning the area of the mower deck, drilled 7mm in the middle.
Spin a nut on the threaded bar and the spring will stretch without any trouble at all.
John