OK, Looking at my Conrail book " Conrail the Final Years 1992-1997 by Withers Publishing, I see :
- most GP38-2 have the two strap signal equipment box. I believe the OSA signal equipment box is the older PRR 3 strap ones. The PSC boxes are the Two straps that you seek- part #PSD56171 unless you have a picture showing otherwsie.
- What's wrong with the molded in casting on the Weaver models? They are well detailed and you best leave them alone. All you really need to do is drill out and use a red LED Dalee Electronics item #542
or an MV lense if you want that marker lite look without the function. https://www.dallee.com/Lamps_Sockets.html
- for the MU hose detail, go with PSC #56187- brass part with rubber hoses and mu connections on the end.
- If you need the 4 prong ones it's PSC #56199
- For the air hose, go PSC # PSH4279
Definitely go Brass with the MU hoses and Air hose. Don't be cheap or you will find your details easily breaking off.
For the Wipers, The irish tracklayer had some coolmodern dual arm brass ones but He doesn't list it in his amazon store. the OSA, Cal Scale and PSC all are older single arm. BTW, you can make the modern ones with a micro drill bit, some regular staples and some T-50 staples as seen on the Lionel oversized C40-8 standard cab:
I hope this helps.