In the 1930s and '40s there were several official trails to Tecumseh that no longer exist (officially). There was also an unofficial trail from the summit of Tecumseh to Welch Mt. That's the one I think you're interested in.
Here's the description:
From the main summit of Mt Tec. the crest ridge can be followed S, without trail, to Welch Mtn....From the main summit of Mt. Tec, follow the ski trail to the ridge S of the cliffs. Heading S, keeping somewhat W of the crest, avoiding two humps [sic]. When above the Tecumseh-Green col, swing SW and drop down to it, finding open ledges and a partly cleared surveyor's line. Follow this over Green Mtn (wooded), thence to an open summit with a fine view (probably Stone Mtn), then over open ledges to Dicky Mtn and Welch Mtn. Distance, 5 miles (4-6 hours). A 1936 description.