Will it make a decent fish oil?

Never had much luck with carp for anything other than using them whole for drawing critters into an area

Not a good fish in my experience for producing good oil. Try some, maybe your batch will be better.

No. Tried carp a few years ago but got nothing but mush.

I have a 55 gallon drum that friends load up with carp they bow hunt. I stagger the barrels so new fish don't go into aging barrels. After a couple of hot summers the original barrel had a beautiful amber oil floating on top. Only added a bit of clean spring water and a lot of patience but I was happy with the finished product quality and smell.

In Russ Carmen's lure making book he discusses carp as a source for fish oil and his conclusion is consistent with Mr. Jameson's -- he didn't find much value in it.

My limited experience is that warm water fish like carp, bass, etc. don't have as much true oil in their body, like cold water fish such as trout and salmon. Catfish may be an exception to the rule. Oh, when they are rotted down they will stink and can cause a rolling reaction by some canines (every dog will roll on a rotten fish they find), but in terms of a valuable lure making product, my experience is the cold water fish are better.