Hi Brian,
just read your post, yeah maybe spring loading isn't the best idea after all, maybe you could use the idea that I had for tensioners for my build but didn't use. The drawings aren't complete, (no dimensions) as I didn't needed to complete them, but it might just get the grey matter going.
best regards, Mark.
p.s. just tried to add the drawings to this post but they are too big (apperantly), so I have put them on my toylander build website, (link under members) in the photo album titled 'Drawings' under 'Base Plate' and 'Slider Plate'.
Mark.