Briggs twin cylinder OHV.
You said in a previous post that no gasket was used just sealant.
You can go to this link and see a gasket set for your engine and the sump gasket #12.
You say you bought it NEW.
Appears Wilbur may have been into the engine and did not use a gasket.
I do not know about those popping sounds you heard unless the engine maybe blowed a head gasket and pressurized the sump and blowed out the sealant?????????? When you get governor control you may still have popping noises?????
Those cracks in the sump may be casting flaws???????????
Now for the governor itself..
Do you have the Briggs Intek twin cylinder OHV SERVICE manual?
If you have done the above static gov adjust and the governor is still not operating do the static governor adjustment AGAIN and tighten the clamp nut on the governor arm to specs. I've seen those governor shafts coming out of the engine slip (rotate) on the arm if you just use a nut driver and/or a weak wrist. Be careful and tighten the clamp nut to specs but do not break the clamp. That Governor shaft coming out of the motor only moves about 45 degrees or little over 1/8 inch rotation on those engine for full governor control on the LONG carb governor lever. You can test the full rotation of the shaft CW and CCW with the 1/4 inch nut driver on the end of the shaft with the engine NOT RUNNING. If the arm slips due to not being clamped good the engine will run wide open. Also make sure the governor spring is connected properly.
I've seen first hand what you describe when the governor arm and or sump has been removed and re-installed due to the arm slipping on the shaft. On some Briggs engines I had to remove the governor arm bolt and turn it around opposite direction so as the lock nut was more easily accessible using straight extensions.
I've even adjusted the Static governor adjustment backwards (so as the governor would hold the engine at idle when started) to make sure the governor shaft is rotating or attempting to pull the throttle towards idle.
When starting the engine after adjusting the gov hold the carb throttle shaft manually at idle start the engine and then slowly let the gov take control.
You can manually keep the engine from over speeding and ruining itself until you get/see correct gov control.
Let us know what you see/find?????????