Pay off HELOC using Social Security at age 67 or delay it for increased monthly benefit at age 70?

I am asking for thoughts around a potential scenario involving husband John taking Social Security benefits at age 67 in order to have a $75K HELOC paid in full by the time he actually stops working at age 70. He would continue working during those interim years so the entirety of his SS benefit could be thrown at the HELOC. We are living just fine on his salary alone now so I foresee no difficulty in actually getting it done.

Wife Jane is older, already receiving SS, and her entire benefit is now being used to pay on the HELOC and her Plan G insurance. The combination of both John and Jane's SS would have the HELOC paid in full by the time John stops working at age 70.

I will provide all numbers if anyone is actually interested in helping me see if this is a viable plan or whether there is something I have overlooked in my number crunching.

I have considered increased federal income taxes and interest savings during the payoff period- our state does not tax SS.

All of our numbers are quite low so the increase in Federal income taxes only amounts to 1766 a year. No increase in state.

Total HELOC interest paid if we get the HELOC paid off by John's age 70 would be $6,784.75.

Interest if we DON'T do this and continue using Jane's SS alone to pay the HELOC is $28,012.98 in interest over the currently planned 10 year repayment period. Current HELOC rate is 6.89% but it is of course variable. That would be a total of $21,228 in interest saved.

But would mean a reduction in John's SS benefits of $500 per month FOREVER.

Even with this scenario's reduced SS benefits after he quits working at age 70 our income would still be $1K a month more than we are comfortably living on now. John has a small pension starting at age 70 that I am not factoring into the decision- it will be used to cover his Medicare Part B and Health insurance Plan G.

Of course the wild cards are terrifying inflation, SS itself, health insurance increases, and potentially low COL increases in benefits.
John is amazingly fit but future health is always unknown.

I think it would be better to get rid of this HELOC and the associated interest as quickly as possible. He'll be working until age 70 regardless and going into the true retirement years with absolutely zero debt seems preferable.

Yet the loss of the age 70 SS benefit number and having the age 67 SS benefit number forever is a bit scary.

If you've made it this far thank you. If you have things you think I haven't considered please tell me. John is just turning 66 so we have a year to decide, watch inflation, etc.

HELOC bal $75K variable interest now 6.89%
John current income post tax $1050/ bi weekly $25K year (he throws a lot into his pension fund)
Jane current SS $1150, $200 to health ins, $950 mo to HELOC

John projected SS-
Age 67 $2100
Age 70 $2600
Pension age 70 $500 mo/ will pay Part B and Plan G.

As I said our numbers are all quite low but we have very low living expenses- home is paid, property taxes are low, and we do not travel.
We have a $10K emergency fund.
We are living just fine on our current post tax income of $25K as all of Jane's SS is currently going to HELOC.

I'm just wondering if there is anything I may have overlooked.