stroke

If you have a couple larger "V" blocks you can measure it pretty closely. A couple pcs of narrowed 2x6s with a 2" deep V in them would work. Narrow the end with the V so it's 1/2" thick, then sit the crank in the Vs so it can be rotated. Measure the from the lower side of the journal to the table with the rod throw "down", and then measure it again from lower side to the bench when it's "up". The difference is the length of the stroke. That should get you close enough to figure it out.