Checking the block deck should be step one honestly, not something you skip because the head got a clean bill from the shop. A pressure test only tells you the head holds coolant, it says nothing about whether the deck is flat or the fire rings will seal against it. Pull a straight edge and feeler gauge across that surface before you bolt anything down, it takes ten minutes and saves you exactly what you just went through.

Put the mower in front on a cheap dolly so you roll it out first.

Man, I learned that lesson the hard way too. After a nasty windstorm took out half a maple in my yard, I started cutting back dead wood every fall instead of waiting for nature to do it for me. Those dead branches are basically a weak spot just waiting to fail when ice or wind hits.