Sorry, I don't have Model 90 to study -- I just posted the old American Rifleman extract. From the parts diagram, it appears that the two screws in question are the key. With them removed, as you suggested, it seems the wood slides forward. If it resists, don't force it -- it's 50+ years old. The wood removal should be the same between single and dual trigger models. The actual dual triggers are similar, see below (the auto safety has been removed from the single). You can see, the M-90 doesn't have traditional hammers, but employs striker-type firing pins. With the wood off (which may not be easy), you should be able to do a thorough cleaning and lube without any further disassembly. From your OP, I'm guessing you're considering refinishing or replacing the wood.
