I would get a measurement from the front of the cab to the end of the hood and compare that measurement to that from the back of the uprights that the loader frame pivots on to the cross member that ties the two sides of the loader frame together. I would want those measurements to be about the same. Every bit that the loader is longer is that much more the loader sticks out front. Also get a width measurement of the front bolster of the tractor and make sure the loader attachment is wide enough. Are you looking for a quick attach type or the old style mounted to the back axle type? I don't know how much size difference in frames there are between the 870 and a 970/1070, but I was looking for a Westendorf WL42 because of the ease of taking it off and putting it back on. My second choice would have been a Miller P12. I also liked the looks of ALO Quickies but they are more money. My dad has a Koyker K5 on his 970 and that seems to be a pretty good fit but not real easy on and off. I don't know what you're uses will be but I would want a bucket as wide as the tractor tires so if you're pushing dirt of snow you're not driving on the windrows left by the bucket. Probably want it least a 7' if not 8' wide. Are you going to want to swap attachments, say from the bucket to pallet forks? If so look for one with a quick attach feature. If you find one, look for repairs made and if they look OK. Check for wear at all the pins. Sight across the top of the frame and see if its twisted. Check for evidence of hydraulic leaks, hose condition, does it include a valve that you can use? You're not likely going to find a loader with the mounts for the 870 so you'll be modifying what comes with it, buying new from the manufacturer, searching dealers, or building from scratch. Is this going to be a do it yourself project or are you going to have to hire it done? Good luck with you're search! It took me about 3 months and had to drive about 350 miles to retrieve mine. Hope this helps.
Kim