I think the problem is the sunroof has been shut for so long its compressed the seal.
There doesn't appear to be any way to adjust the latch so i'm gonna remove the catch from its mount completley and see if i can shim it somehow.
You've got a long time to wait if you're waiting for the warm weather. Its usually the mid week of july isn't it?
What size engine are you building for cabbage?
I've got the stock 1300sp for mine in bits at the mo. Gonna fit a minnow fish carb, 1.25:1 rockers and a set of taper tips for a bit of retro power.