Kitchen wall cupboards

Since removing one of my kitchen wall cupboards (LHS of cooker) in order to fit a new central heating boiler, the other cupboard (RHS of cooker) has dropped by up to 1/2". The two cupboards were screwed to a plastered double brick exterior wall (through triangular metal corner pieces), with a bridging unit supporting a cooker hood. The bridging unit was screwed to the left & right units and not fixed to the wall (and is now only screwed to the RHS unit). This is the reason why the remaining cupboard has sagged. I have placed supports under the remaining unit but obviously wish to carry out a more secure job. Would window frame fixings be suitable in order to avoid removing the unit? I intend to jack up the cabinet using a car jack, redrill adjacent to the existing fixings and then fit window frame fixings. What size would be the best - the unit weighs about 24Kg empty.
Terry D.
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