A very experienced Volvo pro mechanic has an older Haltech, with which he has become very frustrated. He ditched it, at considerable cost, in favor of a new Motec. They sell several levels of equipment I think.

Seems to me that there is another possibility: a programmable Motronics ECU can be reprogrammed on the fly with software from www.bonnevillemotorworks.com - that's Landshark (Jim Conforti). You should investigate that option, I think, because with any aftermarket system you'll have to develop your own fuel and ignition curves. Further, you'd be using the system already installed (granted you'd have to transfer it onto your block) but the sensors would all be there, and you would know they have the range capability that's right for your motor.