You'll find lots of topping lift ideas shown in the gallery, with varying degrees of complexity. Here's what I did at the masthead:
That's a brass snap shackle for removeability, with clear coated cable. I hardly ever need to remove it tho. BTW, that's the windex sticking forward, which I've since turned around so it rests on the eyestrap - easier to see when it points aft.
Similar arrangement at the boom end, but I don't have a picture of that. It's a quick link through the aft hole in the boom end cap (forward hole holds the outhaul bullet block), and another snap shackle. I've never really had any need for adjustability there: when the main is up, the topping lift is just slack, and when the main is down, the boom stays just about perpendicular with the mast. For trailering, I take the shackle off the link and snap it to the Cunningham eyestrap at the base of the mast.