Before you do anything, reattach your engine hoist/lift to the engine as you are going to need to undo and reinstall at least 1 of the adjustable support arms as well as loosen and adjust the positioning of the others so your engine is properly connected, positioned and supported by the stand.
The weight of the engine needs to be fully supported by the hoist so you can safely move the engine around a bit. Safety First!!!
The mount/support arm that you are holding by hand in your 2nd picture needs to be first properly mounted to the stand plate in the same fashion as the other 3, then it can be repositioned and the longer bolt used to attach through extension end of the arm to the block. When you change that arm to become adjustable on the main plate (the way you have it now it freezes the engine position to the stand), you can then shift the engine and arm positions to allow for the 4th arm to reach the opposite mounting point from the lower left of the block. See the 1st pic below of an engine similar to yours mounted an a portable engine stand to see how it should look.
Once you get all 4 arms repositioned and secured to the block, and the bolts properly tightened, then you can remove the engine hoist and allow the stand to support the engine to continue work.
Another IMPORTANT SAFETY point! The pivot/rotating shaft collar of the engine stand has a hole for a locking pin or bolt to keep the engine from all of the sudden rotating and turning upside down on you while working on it. See my modified copy of your pic to see where I am indicating. You need to make sure there is a pin or bolt in place anytime you are not trying to rotate the position of the engine as such a sudden uncontrolled movement can have very serious consequences (think major injury)! Your engine stand should have come with a set of instructions. Please take the time to read them and follow any warnings.
Dan
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)