[quote]The Opel box used in the early Holdens was from the '67 Opel Commodore sixes with identical ratios. Cam-in-head Toranas used the Opel Rekord ( same engines ) version of this box . I understand that the M20 box is identical to the Opel Commodore box.[/quote] my recollection of the 6 cyl opel box was that it was a scrawny little runt and in no way comparable with the m20 aussie 4spd produced from july 1971, it was gm's habit to use the m20 code on their id plate for all of their lowest level 4 spd transmissions, so many of GM's boxes could be called m20 including muncie ,saginaw, aussie 4 spd and opel. the LH photo is the aussie 4 spd which has reverse idler shaft that meshes with the helical cut gear on the smallest end of the counter shaft pictured ,resulting in a moderrn quiet reverse gear. the opel shaft pictured is the puny item on the right not worthy of a large car and certainly not XU1 material, note the outdated extra reverse whining straight cut gear