AMP currently controls 15.71 per cent of Wakefield's shares.
Austron's agreements with Royston, Medusa and AMP will provide that the minimum acceptance condition is met once the formal offer is put to shareholders.
Austron said the certainty that the offer will succeed will not preclude all other shareholders from participating.
Shareholders who tender up to 50.01 per cent of their shares will have those shares accepted under the offer, Austron said in a statement.
All shareholders who tender more than 50.01 of their shares may be scaled down.
Austron said it had no present intention to make any material changes to the business of Wakefield or its subsidiaries.
In May, Wakefield reporterd underlying earnings for March year of $6.52m, up 27.2 per cent on the previous year's earnings.