I did most of the conversion work for Paul Callahan's Life pages, so I can probably answer this.
There would have been some serious difficulties with hosting Paul Callahan's pages on conwaylife.com, because the original pages used a Java applet no longer supported by any modern browsers.
Luckily, thanks to Chris Rowett, LifeViewer made a very good drop-in replacement. Pretty much all that was needed was a lot of careful regexp search-and-replaces, if I remember right.
Other than that detail, Paul Callahan's pages, like many other Life-related websites published in the 1990s and early 2000s, are just a large set of interlinked HTML files. That's a fine format for anything that might belong in conwaylife.com/ref/.
As soon as any kind of server-side scripting or database support is needed, things get a lot more complicated -- the hosting for conwaylife.com is fairly limited (as a fair exchange for not costing an arm and a leg).