I would bet the engine ran with the crack for a long time and will continue to run with it. Mid block, low load, putt around town truck, low rpm, I see no problem with it. If it falls apart when the bolt comes out, now you have issues.
Install a name brand stud, large flat washer, and have the cap milled on the bolt boss so it's true flat ( you could carefully hand grind it flat ), and torque it down. The crack is vertical and not in the bearing area. A stud and nut will torque a little easier then a bolt and not as likely to twist on the cap as hard using a hard washer.
In my opinion,
Joe
