The term 'Nitro' might indicate value range high enough to pay off the Orthodonist and College Student Loans or low enough to make it a display only 'over the fireplace wall hanger'.
In case you haven't bumped into it by now there is a Lefever Forum Website.
Someone there, here, or elsewhere will ask for clear images, stamps, and lots more detailed information than you have provided.
Luck to you,
salty
EDIT: For what its worth, ours is the lowest Field Grade, wih sweat or oil stained wrist, dull checkering diamonds, minor rust stains, tight lockup, shiney bore, uses std smokeless ammunition, 'fits' me well, and has an approx value of 600.00.
It is insured for more than that figure. Don't know what its 'worth' though.
sd.