Trying to fill out wife’s W4. Previously we filled out W4 Single/Zero dependants to overwithhold. I just want to mimic that on the new form. How do I do that?

No.   Your W-4 is just the document that tells your employer how much to withhold from your paychecks.   Your W-4 only goes to the employer.   It does not go to the IRS and does not dictate how you file your tax return.

No. As previously answered, you can claim anything on the W-4; it does not affect how or what you claim on your tax filing (it doesn't have to reflect reality as long it withholds enough to prevent underwithholding penalties). If claiming "single" doesn't withhold enough, you can specify an additional amount withheld each paycheck on line 4(c). In the past, I have claimed 9 dependents/exemptions to get the calculated withholding either at zero or close to it, and then put the exact amount I want withheld on line 4(c). I would have claimed more than 9 except it requires additional paperwork.