I think that is what mine is but I will re-measure mine with calipers today. I had a little chuckle when I found a PDF of the operators manual of the Tie-bar lathes, they referred to spindle bore as " a little over 1 and 1/2 inches" ...no reference to an actual # which I thought strange because the rest of the manual is very precise in content. That manual also offered up that Henley offered 4 different set of collets with their lathes, all for the same spindle just different numbers of collets in the sets so I'm hope-full yours will fit.
A bit of an update; I managed to get the top drive bolted back up to the bed, it hasnt been tightened down yet tho, I need to plumb-bob the cone pullies for line up so the leather belt runs true and doesnt chafe itself on an edge.
So far I have narrowed down manufacture date to between 1907 and 1911 from other ser #'s researched on Practical Machinist (thanks again 140 for that link).