What LW was needing was a Mosqito killer using 1943 engines. That means that should be smaller and lighter . Ideally Fw 187. From the historically available aircraft , i would propose a cleaner Me 410 with GM1. Even better Do335 , if they could focus on the NF variant.
A little bit of telescoping going on here - exactly what is a "Mosquito Killer" and exactly when does the Luftwaffe figure out it needs such a thing? By 1943, the Fw 187 is dead in the water. Not a chance of it being revived and let's not forget that it suffered the same fate as the Westland Whirlwind - it was too limited in scope and size to be anything more than a novelty - yes, Tank and Co redesigned it on the drawing board, but the RLM simply wasn't interested, just like Petter and the Merlin-engined Whirlwind Mk.II - no one was interested in the British Air Ministry.
A cleaner Me 410 with GM1? possibly, but can Messerschmitt spare the extra R & D effort, particularly with the Me 262 undergoing testing, and why would it, with the Me 262 undergoing testing? The Do 335? Too little too late. The RLM and the German aviation industry has made a few too many missteps by 1943 to enable anything beyond the path it was already committed to. Bomber B was dead by then, the He 177 was a BIG problem and would remain so, and what you have left is the Ta 154, the He 219, the Ju 88/188, the Me 410 and the Bf 110. Jets were coming on line, which is certainly a positive, but by late 1944 early 1945 when your Mosquito Killer with its 1943 engines is entering service, the war industry is being pummelled by day and night and the country is under invasion from East and West.