Hi Reverb, I've always turned cyl upside down & set it on large thick block of wood. Set block on concrete floor. Find a place where wood sets flat & doesn't rock.
I use hammer size/weight of carpenters hammer. (claw hammer). The hammer factory used is in drawing in shop Manual
. They do fit tight & need a firm dead blow, not a tap, tap.
I've only done it cold. Heating cyl may help??
I deburr & smooth the bore on cyl & OD of tappet block. I deburr oring groove. There is small taper at the lead in for o-ring to easy by. Make sure this taper is really smooth. I use thin coat of grease as a lube in bore & OD of tappet block. Thin grease on o-ring. ALWAYS USE VITON O-RINGS.
Keep in mind the tappet block isn't straight up/down, but is sloping in cyl, so keep tool & hammer blows at proper angle.
This has worked very well for me several times. I think about the flange breaking off every time, but not had that happen yet.
The block will want to spin as you drive it. As TinkererToo stated you can easily rotate block while it's moving. NEVER EVER attempt to rotate block if it's not moving. I use straight edge through block as TinkererToo does.
I stop with 1/4" to go & measure squareness. Simply putting strong turning pressure on block as you drive it allows it to turn surprisingly easy. I keep measuring as I get closer. If your home & it's not square, put turning tension as you drive it back upwards, then back down. Only need to move it up a few mm. You will soon see how easy it is to align. I shoot for about .001-.002". I feel a very square installation reduces, block, cam/tappet wear.
I've seen blocks installed crooked & the wear pattern on block was decidedly worn crooked. Yet retaining bolt went in easily. There is a lot clearance for retaining bolt, so I don't feel you can really trust the bolt/hole for perfect centering. These little details make a difference on long term wear.