B&S engine, 23 HP, back fire through intake

JD Z425 zero turn mower, mowing and then not.  Back fire through the intake, cylinder to the left facing the breather.  Removed plugs and confirmed cylinder/valves not working.  Removed covers and one push rod is missing, the other is bent.  Presume the missing rod is wound up in the sump but engine turns freely.  Also presume that a loose exhaust rocker bolt allowed the push rod to drop out, this and the back firing, then caused the intake push rod to become bent.  Question, if I separate the sump, find and remove the aluminum rod, look for physical damage to anything, replace the sump - gasket and seals, install new push rods, set all back lash gaps to .004 or .005, lock tight rocker bolts, does anyone see an issue with this plan?  Nothing else appears wrong with the engine.  Some other mentions about valve guides missing or loose but I haven't gotten that far.  Don't see guides as replaceable parts.  Thanks for any assistance.

Thanks AVB for the quick response, 
More information, other head, valve clearance is about .010, maybe .009 but intact and operational, presume that due to the nearly 2 times the clearance and then a loose rocker bolt is the reason the push rod fell out, and no other issues that would cause the rod to drop.  Plan to reset all the valve clearances to around .005.  If I remove the head, not sure what to look for other than obvious damage.  Probably can compress the springs and remove the valves but again, no way to lap the valves or do critical inspection other than look for obvious issues.  Jacks has a head for about 165 or so, also which is #1 and which is #2?  I'm viewing the engine from the front, air cleaner side, and see a left side and a right side.

Thanks Roy,
Any way to confirm if the guide has slipped from the outside looking under the valve spring?  It would confirm if the head has to come off and be removed or replaced, if not pulling the head is a $20 gasket and possibility of stripping out a head bolt.  Don't want a repeat of this issue but like to confirm the need to pull the head.  Still have to open up the sump and find the missing push rod, hoping it didn't damage anything internal.
Thanks,

I have been chasing the same issue on a 24hp. The guide was pushed out so I pushed it back in an peened it in place. I replaced the set of push rods again and went mowing. It was running for an hour or so and the push rods bent again. It was running perfect before that. I pulled the valve cover and the guide was still in place. The valve seems to be seating fine and they move freely. 
 
So why am I still bending push rods?
 
Thanks for your help!

I have one on order.. $147. I should be mowing again this weekend. 

Of all places Walmart. It comes on Thursday. I will let you know how it went.

That's just a bit mean, on a small business parts house forum and you get parts from Walmart.  I understand and don't know how Walmart can provide a part that they probably have no idea what it actually is, but they can get it to you cheaper, somehow, and it all probably comes from the same place, overseas!  Thanks,

He actually paid the suggest list price and the part would be coming from an US Briggs distributor. Now Briggs is most likely getting the heads from China however.
 
That 84001918 (#1) head current costs me $115 from my distributor. Jack's price is above my distributor list price. Many other sites are higher too. Even Power distributors is $133.11 and it is dropped shipped. Now the two distributors that I prices from only sell to resellers (repair shop and retailers).
 
The only thing Walmart can provide is free shipping. Most likely Walmart will not honor the Briggs warranty either like my distributor will not honor the Briggs warranties. Claiming it is a Briggs warranty policy and the local dealers are to honor the warranty. Guess what the local dealers around refuse to honor the Briggs warranty unless they sold the part or engine directly.
 
Last year I had to pay $130.50 for the 84001919 (#2) head. And originally it was suppose to be both heads then Briggs superseded the PN to the current PN make the price for one head. Good thing I didn't pre-sold the head as I would got burned for $60+ dollars.

I know I do if the parts exceed 50% of replacement of the equipment or engine depending what I am working on. That is why I still have 84001919 head as when I pulled the head the cylinder was shot and the engine was needing to OS pistons. That plus the head exceeded the threshold I have set so the customer called it DOS. Besides the mower looked like had been to heck and back. It went to the recycler.

It was a $30 difference between Jacks and where I got it. Gotta save a buck or two these days.