I can't help you with the power valve question.
Long rods are what they say a longer rod than stock. It improves reliability by decreasing the angle on the bearings. It may give you a tad more torque, but nothing to write home about.
A stroker will give you a big increase in power and torque, as for reliability I don't know. The crank is bigger in diamater causing the pistion to travel further inside the cylinder. Increasing the displacement and bringing in more intake and puting out more exhaust. With a stroker crank the bottom of the case needs to be trenched to accompany the bigger crank.
I'am new at this so I may be work with some things and I appoligze. Please correct me if I'am wrong, but I hope this helps.