If this was reported on a Form W-2 rather than on a From 1099-R, it was a distribution from a nongovernmental 457(b) plan that was not eligible for rollover to a traditional IRA. Any deposit of this money into a traditional IRA would be a new, regular contribution to the traditional IRA. The income on a W-2 that would support such a contribution is the amount in box 1 minus any amount in box 11. Being a nonqualified plan, I would expect this W-2 to have the same amount in box 11 as in box 1, meaning that this was not compensation that would support an IRA contribution, so unless you have other compensation to support the traditional IRA contribution it would be an excess contribution subject to penalty each year until the excess is resolved.
