Having reviewed this on May 16, I conclude it is too much of a mashup of several questions I had in mind. Therefore, today I have resolved to edit again. Until that edit is complete, please pardon the confusion.
After a helpful comment from goldilocks, I have reworded this post. I may need to edit it again, with your helpful comments, to make it more useful for others.
I have read several blogs and forum posts on getting the Pi4B raspbian install, to run in 64 bit by swapping in a 64 bit kernel and or modifying the boot partition. There always seems to be more complication than necessary, with dreaded secondary issues of software in the repositories being for the 32 bit kernel (if you try to hack in a 64 bit kernel from some other distribution). And yet, there is the 64 bit ubuntu image available for Pi4.
My newbie mind may have misread or misunderstood, but I imagine there should be a very easy way to do this that uses the smart package handling features of debian linux, without having needless complications of arm32 libraries not yet available as arm64 libraries.
For example, I have several pi 4B's, and intend to install the 64 bit ubuntu on them, possibly only a minimal or server image. A full 64 bit GUI install may be in the future, but is not the need of the current projects. Assuming that anything a Pi compatible arm64 image would install would also be Pi compatible arm64, running in true 64 bit mode, already... I understand that any 3rd party non-pure-python libraries from the 32 bit userland, that are not yet in the 64 bit arm repositories, may have minor to serious issues on such a 64 bit python3 that would be installed with the 64 bit ubuntu, but if I am very wrong on that, do please advise.
Would a pip install on a 64 bit ubuntu Pi4 system, know enough to install for 64 bit, if there is no arm64 candidate found, and I have to add a 32 bit arm repository just to find that library?
Is there some tech article on a procedure to get a 32 bit library, not yet available in a 64 bit repository, to work on a 64 bit system? Whether with apt or pip?
I would like to know if I will need to do some fancy footwork on a pi 4B, running 64 bit ubuntu, in order to ensure that packages currently only in a 32 bit arm repository, or in 64 bit x86, but not yet in an arm64 repository, will be reasonably able to run in the 64 bit environment, with the limited skills and knowledge of a relative newbie.
Worded another way, is there some definitive blog or tech source that makes the necessary steps simple for a relative newbie, to make the plunge into 64 bit arm (on the Pi 3B+ or 4B) full on, as painless as possible?
If there are some blogs you are familiar with that address all this, that I have missed or perhaps misread, feel free to include links to them in your answer(s). I have no doubt that where I am ignorant on these matters, it is plain to those of you far more knowledgeable and experienced. I am hoping an answer here will help other newbies understand the more major issues that may be encountered in making the switch, and to get all one's ducks in a row before committing to the switch, at least until such a time that raspbian64 appears on the downloads page.