Walter Alexander decided to sell his business to the SMT group in 1929, and through this action, received access to a vast supply of resources and services.

[3] Coachbuilding work had initially taken place at the company's main bus garage and works in Brown Street, Camelon, but it outgrew this facility and in 1930 a bus garage in Drip Road, Stirling was converted into a dedicated coachbuilding factory,[3] although a few bodies for Alexander's own fleet did continue to be built at Brown Street in the 1930s and '40s.

[4] Although Alexander remained the largest supplier of bodywork to what became the Scottish Bus Group, the independent company also began to broaden its customer base.

In 1969, the company bought out Potters, a bodybuilder in Northern Ireland, and set up a subsidiary Walter Alexander & Co (Belfast) Limited,[2][5] and within six years started selling buses to the Far East.

[6] By 1983, the company was the largest supplier of double-deck bus bodies in the world,[7] and a year later it won a British Rail contract to construct 25 Class 143 carriages.