As a software developer I think your attacking this problem from the wrong angle... Developing for the lowest common denominator will always lead to poor/mediocre results and frustrating support. In this case developing around the small minority of "classic" users will hinder the majority.
Make a *great* site with the newest and coolest tools preserving the content as best as possible. That should be goal #1.
If the site was meant to be viewed on classic hardware solutions will come forward (heck maybe even a new browser), and if not then there was probably never much interest anyway.
Besides simple/older browsers could always use something like
http://mowser.com/ just give it a site and it renders a simple HTML version removing unnecessary code, CSS, images, etc. Meant for mobile users, but I'm sure a possible work around for the hardcore classic users who have to use their classic systems on the web.
I think developing for the small minority, that do have some possible workarounds, is only going to limit you in the long run and cause increased frustration. And for what?! The 5% of people who might use a classic amiga to occasionally access this site? Why bother...
My $0.02 anyway...