I have a similar situation with a long torso and wanted to find a pack frame that I could use with load lifters. One of the things that I did was to extend an ALICE pack frame by welding two frames together. I was able to use MOLLE pack straps and hipbelt with this frame, although they are relatively heavy. This stuff hasn't been hard to come by or expensive, so it might be worth a try. You can see pictures here:

http://www.pbase.com/wgiles/alice

I cut the frames with a tubing cutter and had a local welder weld them together and then riveted the center straps together. The MOLLE straps and belt are heavy, but comfortable. I later found a load carrying harness made by Condor, that I could cut down and use for the shoulder straps and hip belt. I then started making my own frames with tubing and hardware from the ALICE pack frames. All of this has worked pretty well, but I've moved on to other designs and started sewing my own packs and straps. I have used these pack frames for heavy loads over short distances, mostly packing out glacial stones for landscaping.