Older houses, especially if basement floor was originally dirt,
often have less than ideal floors.

Yep, sounds like the basement floor in my in-laws house. I don't know if
the floor was ever dirt, but the concrete floor is really rough and uneven.

with the home center screw poles

I can't say I've ever seen the screw poles at the home centers. Where are
they typically located in the store?

extracting and replacing of the beam, which is a multi-strong-man job
not a husband and wife thing.

In my case, the 6x6 beam is only eight feet long, half of which has already
rotted and been cut away. I'll probably cut out the remainder in chunks I
can get out easily.

As for the replacement, I'm planning to install built-up beams made of four
2x8's. Easy to lift into place, and all access is clear from inside the
basement. The original 6x6 beam has a 2x6 on top which makes the total
height exactly 7.5". The 2x8's should be a perfect replacement.

Anthony