how much slip yoke play

I do not have a manual transmission but I can't think of any reason that a manual would have any different slip yoke travel. When I had a driveshaft made for my auto the shop stated that 1-1 1/4 inch of travel was all that is needed.
If you remove the rear universal straps and check your travel at the tail shaft ,you shouldn't have anymore than an 1-1 1/4 inch of travel. Mark the slip yoke at the tailshaft and then push the slip yoke as far as it will travel into the tailshaft and mark it again the distance between the two marks is the amount of travel you have. I used a black sharpie to mark mine. Hope this helps with your manual tranny.