Windows 10 Pro on 3660 that came with Windows 11 Pro

Yes, you can access to a comprehensive list of all available Windows 10 drivers for your Precision 3660 here https://www.dell.com/support/home/en-us/product-support/product/precision-3660-workstation/drivers

It should not affect your warranty or support contract.  However, Dell support may require a reinstallation of original shipped OS (Win 11) to initiate their troubleshooting.  This should not be an issue as you can pull the original Win 11 boot drive for preservation and installing Win 10 Pro on your own new drive. 

Thanks! I understand you are recommending pulling the original boot drive for preservation. Could I instead create a system image to archive and then use the existing boot drive for installation of Win 10 Pro? For my Win 10 Pro installation, can I pull an image from the Dell website that will access my (Win 11 Pro) mobo product key such that I don't have to purchase a new Win 10 Pro license?  Everything I've read so far talks about using Dell "SupportAssist OS Recovery", and using that tool I seem to only have the option to reinstall Win 11 (or Ubuntu). Googling seems to indicate I can use a Win 10 key to activate Win 11, but I will be trying to do it the other way around.

Pulling the original shipped drive for preservation was for an easy and convenient method.  Of course, you can certainly make a drive image for preservation and wipe it clean for use with new Win 10 installation.

I suggest to create an installation media (USB) with Windows Creation Tool as it would have the latest build and can be made at the least time.  Remember to delete every partitions on the drive and allow the process to prepare the partitions.  The license is embedded on motherboard and be used during installation and activation without users intervention.