I've got an Armalite LEM15A2.  It's a carbine with the longer handguard.  I was going to get the accessory rail to mount on the top on bottom (economical alternative to replacing the whole thing).  Problem is, the longer handguard get narrower from the receiver end to the firing end, so anything I mount with be at a slight angle.  This makes a difference to me on two issues.  Tactical weapon light and optics.  I was going to mount an Aimpoint forward of the carry handle but the angle will probably prohibit that option.  

Any suggestions, short of buying a multi-hundred dollar replacement handguard?

Thanks.  That's kinda what I was thinking.  I also kinda suspected that mounting a rail on top of my current handguard may not be feasible as is because the guard has a little bit of play, not really ideal for a site.