**Tax Year 2018 or earlier** Can I write off a disbursement from my 401K paid to my ex-husband in our divorce through a QDRO and show it as alimony paid?

You cannot deduct it as alimony, unfortunately.

To be deductible as alimony, it must be made in cash and must be classified as alimony in your divorce.  An allocation of 401(k) plan is considered property settlement, and property settlement is not alimony.  

Below link, page 18 discusses the situation in detail: 

https://www.irs.gov/pub/irs-pdf/p504.pdf

Benefits paid to a spouse or former spouse. Benefits
paid under a QDRO to the plan participant's spouse or former spouse generally must be included in the spouse's or
former spouse's income. If the participant contributed to
the retirement plan, a prorated share of the participant's
cost (investment in the contract) is used to figure the taxable amount.
The spouse or former spouse can use the special rules
for lump-sum distributions if the benefits would have been
treated as a lump-sum distribution had the participant received them. For this purpose, consider only the balance
to the spouse's or former spouse's credit in determining
whether the distribution is a total distribution