I was going to mention that Char-Lynn might have a hydraulic assist motor that would fit between the end of the shaft and the steering wheel, but the broken steering box probably rules out that option. Maybe if you replaced/repaired the box first, then went the char-lynn route? Downside is that it raises the steering wheel up a few inches.
Although I don't see an entire kit listed for your 1700, maybe these folks might be able to help: Power Steering Kits