A 25.4mm post is a relatively heavy gauge steel, as it would translate to 1.5mm wall thick thickness, allowing for a standard 0.2mm diametral clearance. Generally, bicycles with seat posts in this size are constructed using 1020 steel, which technically wouldn't even be considered a high tensile steel alloy.

A 26.4mm post on the other hand, would indicate a significantly thinner 1.0mm wall thickness. A range of 26.2mm - 26.4mm is typical of lightweight, high tensile steel alloys used by Italian manufacturers in the 1970s and 1980s. During the boom era, it would have been found on mid-range models but by the early1980s had trickled down to upper, entry level models. A number of manufacturers, marketed these tubesets under proprietary brands but during the 1970s boom era from which the Torpado appear to be, the most popular Italian tubeset manufacturer offering main tubes with a 1.0mm wall thickness was one marketed by Falck. Consequently, Falck would be my leading candidate. Columbus would eventually offer a high tensile steel tubeset, Zeta, with a 0.9mm wall thickness and typically employing a 26.6mm seat post, but it did not debut until circa 1980.