I did my 235 years ago and all I did was drop the rear main bearing cap and push the old seal out of the top with a piece of dowel. It was a neoprene seal. I did not lower the crankshaft.
Now here is a trick. When you install the seal stagger it so the butt ends are not in line with the split in the bearing cap. In other words push the top half through so that it hangs out the bottom about 3/8". That will also give you a space at the opposite side in the top. When you put the bottom half of the seal in the main cap stagger it the same amount so in effect a portion of the seal will project into the upper half and you will have a space in the main bearing cap where the extended seal from the top will fit. When it is done there is no gap on the main bearing cap for the oil to leak through. When the oil works its way through the gap between the main bearing cap and upper part it will be met by a seal and the oil will not pass it.
Perhaps a bit difficult to understand as its not easy to describe. A drawing would be worth a 1000 words in this case.

1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice