How handy are you w/ welder and torch??? If you are right handy-- you can make anything fit!! If not-- stick with the ones made by mfgr. Or hire someone who can weld.
Also , I gave a brief description of how I built one in an earlier post- see 'Where can I find teeth for toothbar??' The warehouse where I bought the materials for the bucket I built has built a lot of bucket for Bobcats and other eqipment, too. So I listened to thier advice on 'how to'. Check with welding shops and machine shops in your area to find what they can help you with.
As to 'light duty' vs.'heavy duty'-- can you say what is the approximate thickness of the metal of the existing bucket??
The bucket I built is from 1/4" material and I haven't bent anything YET with 70hp. The approx. dimensions are 84"x28" x28"!! Works great for snow, good for dirt, take small bites in gravel!!!
Some of the questions you have to answer for yourself as I know nothing of your ability to cut and weld. Loaders are like everything else-manufacturer specific- I.E. -Green ones don't fit blue ones,nor orange ones, unless you can fit them yourself. Hope all this helps.