O&N are pretty much the only ones to consider. They now do a Non-Pressurised conversion.
it is still mega $$ as far as I am aware.
Yes with the P210 Silver Eagle conversion there was some recent MAJOR issues with the BEW of the plane making it almost useless.
I understand O & N are doing some major works in reducing the BEW.
The Non Pressurised conversions may not have that problem but I have not heard of anyone doing one.