Yes, Tone --- after measuring it up there wouldn't be enough gain to make it worthwhile.
A little trick I do when long stroking HW35s to check if the cocking linkage will still work at a longer stroke is to remove the mainspring and wind out the back block by the amount I'm adding to the stroke, and check that it still cocks.
That's to say if I'm stroking a synthetic sealed HW35 from it's standard stroke of 69mm to 71mm I unscrew the back block by 2mm and check that the gun still cocks.
Having just remembered this trick I'll have a little play with a HW50 this afternoon and see what it can be stroked to.
All the best Mick