WooHoo!!! Success!!
Updated Blocs earlier then opened my existing file and exported it as a Pulse 5 theme. I then downloaded @pulsecms new 5.1 version. Took a backup of my so-so site, then deleted everything from the server. Did a complete fresh install of Pulse5.1 CMS, white labelled it, then installed my Blocs template files. Copied the blogposts from the backup I took, to the site and bingo!
Everything works perfectly now. Linked images, file downloads, links to files, no space above the footer from the back to top button. Most excellent!
Thanks for bearing with me, and for all the work you’ve put into resolving the technical challenges we’ve had over the past couple of months.