The nicest solution I have seen is in the two attached pictures. All I have seen are the two pictures but it looks like the way it was designed to work is when the canopy latch handle is in the spring loaded closed position (3/8”canopy latch tubes extended fore and aft) the pin that is part of the stainless steel weldment that replaces the aft canopy latch tube (C-408) engages the stainless latch in the partially open position. The added benefit of this design is that if someone were to allow the canopy to close without rotating the handle against the spring to the open position it would engage the latch before the canopy latch tubes made contact with the fuselage at the forward and aft ends of the canopy. This is something that can happen easily if you don’t properly brief anyone who may attempt to close your canopy and there are many RV-4’s out there with the scars to prove it. I wish I could take credit for this, but I stumbled across these pictures after I had already completed my hold open feature. I will send what I did in a separate post to give you another option that is simpler to fabricate but maybe not as feature rich as this one.