You can use German HO with Peco OO which is HO anyway as long as it is code 100, I have done this in an earlier model railway as I liked some points they produced, in fact even if you go code 100 Peco but later want to go code 75 then Peco produce a connection piece that allows this to be done.
Rail joiners for code 100 all types I have as yet come across - you can use Peco, rail joiners for code 75 are smaller however.
Rail joiners for code 100 all types I have as yet come across - you can use Peco, rail joiners for code 75 are smaller however.