Gas to Propane generator conversion

[GMP]

I have a new Generac I'm considering doing this conversion on. I have a 500 gal in ground tank that would be easy to tap and avoid the hassle of gas availability in a future outage like the one I just went through. I've been looking at a few kits available, but they seem to be a little biased with a big bright picture but no hard facts relative to long term results. I'm concerned about effects on the engine such as valve damage from running a fuel it was not designed for. I know the power will be slightly less due to the slower burn rate. This can be mitigated if necessary with a slight timing advance. Any practical info and experience will be greatly appreciated.