Changing spark plugs IMO usually waste of money. 99 times out of 100 all it needs is cleaned and gap checked. plugged back in and cranked or pull the rope and see if it got pretty blue spark. IF so it's good reguardless how old it is. I had spark plug in for 15 years all I do is clean it check gap.

As far as the bent crank shaft ususally it's cheaper just to get another mower unless you have one laying around to replace it or the cost of the crank maybe more than the time, cost and effort is worth IMO.

1. What indicates the mower is running hotter? Have you adjusted the carb leaner possibly? Have you pull the starter cover off to verify the head's cooling fins are not blocked with fine grass from mulching? If you hit something to bend Etc you might have damaged the flywheel key (thrown the timing off to cause it to run hotter). Have you checked the key?

2. Are you positive the crank is bent vs the blade? I think some shops will have jigs to straighten shafts w/o removing then. If it's not a slight bend or reasonable in cost with a satisfaction "Clause" I w/n attempt it. Be Safe In Whatever You Do!! loger

There's an art to it, but cranks can be straightened with a sledge. Of course, I've never done it.

I have replaced a few 1970 - 1990 and it's not a hard job on small Briggs (Hor & Ver shafts). The challenge was to assemble the pre cleaned disassembled engines in one hour and start them. The Hor shaft was the best choice of engines due to it starting w/o a blade. The heavier flywheel was enough centrifugal force vs a kick-back. A Yearly Task, in a Small Engine Workshop. loger

Using a a search engine and plugging in the actual Briggs part# from their IPL, apparently that engine comes with 2 different plugs.

It seems the more "exotic" version is for the easy start engines.
I doubt it makes a lot of difference.

Some stock have the thin electrode plug. Like Bill says, no difference to be found in performance. I put in Briggs branded plugs by the box load. They have the thicker electrode btw.