You can also make removal and installation a bit easier if you can rotate the crankshaft. Normally you'd need to remove the rod caps and push the pistons up and out of the way. Just remember to replace all rod caps on the proper rods. You will get a bit more leeway if you remove the transmission as Phil mentioned. As Jerry said, there's quite a learning curve.
Before you do all this, there is another way which might work for you. Remove the rear bearing cap and loosen all other main bearing caps. Pull the crank down as much as you can. Then remove the stainless steel stiffener piece from an old style windshield wiper (maybe like this one:
https://www.tricoproducts.com/products/factory-performance-wiper-blades/trico-classic) and grind a taper on one end of it...just taper one side. Now remove the rope seal from the lower half of the rear main bearing cap and measure the length of the stainless steel piece you have there...make sure it also just fits into the lower part of the seal groove. Now with the angled part of the taper you ground facing the rope seal, gently guide it in on the back side of the upper main seal. You will need a small hammer to tap it in all the way around. The taper is to keep the piece from digging into the old seal. Once you have it all the way around, replace the rope seal in the lower main bearing cap as per GM instructions, trim it leaving only about 1 to 1.5mm proud at each end and replace the cap pulling the crank up. Tighten all other main caps and say a prayer or three.
Good luck!
