The 450 has a larger sail plan, so the engineering around the size of the sprit and its swivel and its stays may be different. So in order to check this measure diameter of sprit, diameter of stays, diameter of swivel bolt. The stays may be too short, but dyneema lacing may compensate.
I'm in the market for a bow sprit for my lagoon 450 f 2014 and am wondering if one from a 440 would fit, as there is one for sale.
The only difference I see is the attachement to the crossbeam is a rail on the L440 whereas it is fixed on the L450, which is fine. Other than that it looks ot be made of the same 80mm x 2mm aluminium tube. Check this: Clapotis Adventures : GENNAKER set-up
I am doing pretty much the same mod on my l440.