yanfly has moved, and on the main side there are links to the new places - it's just the direct links on the subpages that are dead.
that said, the most commonly used english sideview system is battle engine symphony. again its direct site is dead, but with that name you should be able to find the github director that now contains all those script files.
There are a few other sideview systems as well, but the next popular one (tankentai if I remember correctly) had always the problem of instructions in japanese only.
that said, setting up a sideview system will always require some advanced knowledge. If you have no scripting knowledge you can try to follow the link to my tutorial "how to use a script" in my signature.
Failing that you might decide (if you have the money) to upgrade to MV, because MV has a native sideview that can be used without scripts, and if you are willing to wait there are sales several times a year on steam. And MV comes with a script for Ace that transfers MOST of the data of an Ace game (but not all, you would have to rework some parts)