As for the twin rating. Yes Cessna hoped to get away with it, but the Faa had other ideas. Therefore there is an Faa only twin rating for CLT (Centre line thrust) twins, restricting operation to such. But with the same hours and cost as a normal one, there little point in it. If you fly in a G reg, it's the standard twin rating, as that all that available.
I suppose the other question is , what are you going to use it for. It must be for display with the hope of earning some revenue, otherwise why else an O2 and not a 337. Do you understand the operation of that, obtaining a Da, earning revenue on a CPL against operating as a limited company and getting paid that way if you don't have a CPL. Plus of course how all this effects the iarcrafts registration.
The other sore point I found was concerning VAT. I was going to keep it in the N reg, on a utility catagery. But as your basing the aircraft in Europe, you HAVE to pay VAT on import. But even as a VAT registered UK Ltd company such as I am, you CANNOT claim this as input VAT. Simply because you don't legally own the plane, the US trust does. Plus the fact that used military goods have a different import code and valuation system from normal aircraft. The fun goes on.
What else might you not know. The engines only have a 1500 hrs tbo, The props are unique to type, so harder to get a bargain.
Have you seen your aircraft yet. There are still plenty of near stock ones about, with very old or minimal use radio fits !
Do you know about Donald Neiser, he has several projects and plenty of spares..
The other trick I forgot to mention is a little safety matter. Yes the 337 series CLT is much safer than a side by side twin when operating on one engine. But it has a flaw. Depending on MSL and weight the single engine performance in fair to very good, EXCEPT when operating the landing gear. Due to the drag caused by the clamshell type rear gear doors, you will sink 200 ft or so (more at a higher MSL) and you can't do anything about it. So with an efato in some hot and high parts or even partly so, you could have a bad day. There is a mod to solve it, but that would detract from the genuine O2. It's a Faa only (can't use it on a G reg) STC'ed gear door deletion kit. Which means you loose the doors and fit a small fairing the the wells instead, it solves the problem or negative se climb. It's available from a company in Florida, let me know if you want the details, they also sell the clear view doors and some other 337 parts, but they aint cheap.