Wish I had a solution for you. But I know of no slider type sight for recurves. Spot-Hogg makes a bracket that drops (or raises) any sight a 1/2 inch if that help,. which may alow you to use one of the sights you mentioned.
In my neck of the woods a sight on a recurve puts you in the same class as a compound anyway. In my opinion I would look at the recurve target sights even though they are'nt sliders, but screw adjustment sights. I've shot a 64" recurve for a few years in 3d, never has the lenth of the bow been a problem. I don't think you need a shorter bow. Mabey lose the long stabalizer for a shorter one.
I'm assuming, that your 3d courses are the same as mine in clearance for the bow. Yours may be different in reality. Welcome to 3dshoots.