John...I have told you all this before. Isolation excercises for the quads are pointless for what you're training for IMO. You want strong powerful legs for fighting, you're not a bodybuilder so why bother with silly isolation exercises.
Don't get me wrong I'm a firm beliver in that even isolation exercises can cause muscle growth as long as you are using progressive overload and you are meeting all other requirements ie diet, rest, sleep etc etc but you're not training for growth are you ? Surely your calories will be way too low seeing as you are losing weight rapidly.
Your quads will get plenty work from all the other stuff you do. I know you said you couldn't stop doing curls cos' everyone likes big guns ( which is the faggotiest thing I have ever heard you say ) but now you're practically saying the same for your legs. Biceps will get strong from the deads, chins etc that you're doing so curls are just pointless ( especially as you're dropping weight ) and so are leg extensions. I know you can't do full squats with a barbell but you could try unilateral dumbell squats, jump squats with lightish weight, dumbell step ups etc.. all a lot more functional than just knee extensions.
I do agree with leg curls being quite useful though as the average persons leg workout neglects the hammys quite a bit. Lots of squats, lunges, leg ext etc.. and the odd leg curl at the end, very rarely see people prioritising the hammys or doing sld's, glute / ham raises etc...so I guess something is better than nothing.
Hope that helps curl boy.