Does anyone know if the two heads are interchangeable? I have a 1991 300D with a 2.5 Turbo and I have come across some non turbo heads. Will they work?

Will it fit? Yes.
Will it work? Yes.
Is it optimal? No.

The turbo head has a different valve configuration, different coolant flow configuration, and a different prechamber size/design. Stick with a turbo head on a turbo engine.

You didn't specify why you're replacing the head.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thank you.