These headers having 3 tubes go under the drivers side steering linkage are the hardest to install. Without a lift, there a super PIA to put the drivers side in.
Normally I’ll do the driver side first since the passenger header can stop the amount of room available to tilt the engine over.
I suggest taking the passenger side header out and installing the driver side first. Remove the starter before installing the header.
The drivers header design is huge (as your finding out) and a massive PIA to fit in. What I have done in the past is;
Put the car up on the highest position on the tallest jack stand I had.
Keeping the passenger side motor mount bolted in to provide a pivot point, placing a 4X4 (or multiple 2X4’s) under the oil pan or balancer to use the floor jack to raise up the engine.
Since the passenger side acts as a pivot as the engine raises, this opens up the gap like a clamshell.
Leaving the studs in on each side of the cylinder head will allow you to hang the header and then use a nut to put on the end of the stud to stop the header from falling off. Loosely install the nut. Only a few threads are needed at this point. Just enough to retain the header on the stud. Turn the nut on the stud enough until the stud sits flush with the outside of the face of the nut.
Once both side of the header are on the studs with nuts installed loosely to prevent the header from falling off, lower and reattach the engine into its correct spot. Move to the passenger header and install it without the oil filter.
What are you doing for an exhaust system?