Basis

The 71K would not be basis in total for sure, as you said he paid taxes on the  distribution. You pay taxes on the portion of a distribution that was not basis, so at least some of the distribution and likely all of it was not from basis.

His basis would be the contributions he made to the plan that were not deducted from his taxable income, if any. Normally when you contribute to a retirement plan, you do so from income that is not taxed, as is the case in a 401-k plan. Your contribution is deducted from your wage income, so the income it came from is not taxed.  Another scenario is when you contribute to a pension plan, an IRA for instance, and you deduct the contribution from your taxable income. Again, the contribution is from income that is not taxed. You can, however, contribute money to a retirement plan, a Roth IRA for instance, wherein your contribution is not deducted from your income. Such contributions would create basis in the retirement fund, so your basis would be the total of such non-deductible contributions.

I'm not sure how your husband's contributions go into the ESOP, so I can't tell you if they created basis, but if they were from income that had been taxed or weren't deducted from his income when contributed, then you would have some basis to the extent of those contributions. But this is rare.