If the spring load collar keeps working loose, could you use a bit of threadlock to keep it in place?
The "wag" you describe, sounds like something may be worn somewhere, pivot bushes, washers, swingarm bushes etc.
The adapter that someone had made up for my 857 allowed the use of a Fox Float shock with 165mm eye-to-eye measurement.
The drawings for the adapter were posted on here and also the idriders Proflex forum, so have a search around.
The Risse shocks occasionally come up for sale used/2nd hand, so keep your eyes open.
The Risse units seem to be quality items, and for a new shock not priced too badly when compared to Fox et al.
If you have a Noleen NR2 or NR4 I believe a motorcycle dealer "Mick Gardener Racing" can rebuild the shock for around £30 or so (they are an Ohlins dealership), so that may be another option.
_________________Bikes... 1993 Orange Prestige, 2016 Boardman FS team.RIP...[url=http://www.retrobike.co.uk/forum/viewtopic.php?f=6&t=301709]1988 Tushingham B52,1988 Stumpjumper Team, 1991 Scott Pro-Evolution,1992 Kirk Revolution, 1993 Klein Attitude HLF, 1994 Univega Alpina 5.7,1994 Dyna-Tech Diablo, 1997 Pace RC200 F6,1997 Proflex 857,1998 Kona Lava Dome, '01 GT i-drive 5.0, 09' Orange P7, 09' GT Chucker, 2013 Planet-X Pro Carbon, 2013 Ghost ASX.