What size impact driver? A 3/4" would probably work @ 90PSI or higher; otherwise, you need a longer breaker bar or tube. It it's rusted on, penetrating oil and a little heat should help.
Mine only go upto 120 lb.....luckily my neighbour lends me engineering tools and I lend him construction tools...fair exchange...!Ian
Now you have to find a torque wrench to do it up again, unless you have one already :congratulatory:
Though you could use that impact gun that you borrowed - are they controllable ? I have no experience of them.
Bob