The tilt latch can be purchased from your local trailer parts supplier (normally spring loaded) or you can fabricate one as below. Weld the latch to the drawbar along the length of the latch only. Do not weld across the ends of the latch.
If required, packers can be fitted to the front chassis crossmember angle gussets to reduce the gap between the gusset and the latch pin. Allow a little clearance for ease of use (1mm).