recently asked about using PropBASIC with Viewport
As I recall, v4.82 was the last version of Viewport that worked reliably. @Mickster
may have had success with a later version.
Here's some other useful links about using PropBASIC with PropellerIDE or SimpleIDE instead.
Bean did a fair bit of work with the SimpleIDE integration most recently, and has provided some nice demo code too !
(I thought someone had further elaborated using PropBASIC with notepad++, and had created a keywords file. Just can't find that right now!)
Finally, here's the Parallax GitHub for PropBasic. Binaries are included, the latest version being 1.48.