Option 1 use genuine 250 rear lights, about £550 a pair, as they are about 2" shorter you will have to reshape both rear wings, lower the top edge and probably the boot as well to get it to look correct.
Option 2 3D print a new rear lens, have heard this so many times, whoever is going to print them soon goes quiet.
Option 3 Chop up and glue 2 lenses up to produce a smooth lens, this has been done and looks good but I have never seen a close up picture
Option 5 Learn that it is a BMW Z3 (albeit a pretty one). Fine to spend thousands on door & boot handles etc but do remember the windscreen is the biggest giveaway and you simply can't change it.
Hey Steve and loyal readers...
Almost nobody who asks about my 250SWB has any idea it is a Replica, apart from the occasional car buff. Unless you are a Ferratic or a Fanarri (my names for a Ferrari Fanatics/Fans) you would never know a lot of the bling is Mini, MGB, Alfa Romeo, TR6 and of course BMW Z3.
"But", I hear you yell, "the quarterlights and windscreen rake give it away" or, "that does not sound like a Columbo V12", or "those brake/clutch/accelerator pedals look modern (ish)". Again unless you are a Z3 aficionado, Ferratic or general massive petrol head nobody notices, all they see is a great looking car that sounds like a wailing banshee when you get a move on, starts when you turn the key (unlike the original), goes, turns and stops when you ask it to and is a real hoot to drive if you do not mind your car getting more attention than you and even being cheered by people in the High Street.
So in my view, there is no real reason to go for original Ferrari lights / other parts or exact replicas for all of the problematic reasons mentioned by Steve above. The cars look fantastic without and they are not Ferraris!