I've done quite a few conversions on early 90's Toyota vehicles with zero issues. I have done a conversion on a 68 Chrysler 300 and retained the original hoses,drier, and compressor. The owner has been using it for 3 years with no issues at all.
The automotive industry was putting out some ridiculous claims that your system would be ruined and you have to change all your rubber components before you make the conversion. It's all just a bunch of propaganda to make you buy more parts $$$.
I have had good results with all my conversions
Gus