I've worked on a bunch of this , and if you can eliminate any / all of the polybutylene .
If you can not , next is avoid sharbite - it can easily "bite" you in the ass .
There are , and hard to find crimp adaptors for POY to PEX , I have found them at Home Depot's that were near mobile home parks .
And lastly , the best [ by far ] the crimps to use are the , dang can not recall - it was brand specific , crimps that used short pieces of PEX and the tools would stretch the PEX collar over the main PEX tubing & fitting , and now there is a couple of companies doing this .
85 Excella , 31' , electric brakes , R. twin [ would like it to be a single ] , future upgrades , composting toilet [ replace black water tank with a 2nd fresh ] , solar power , instant hot water heater .
Tow 94 Dodge Ram , 4x4 , Cummins , AT .