The second V8 Crossfire ever built was done by one of our members in Germany. He used a CLK55 as a donor and swapped everything that involved elecrtrical so he has a great running car with no programing or other issues. The 55 n/a motor is a great choice. But don't discount the 500 engine I am running. Every SRT owner that has ridden in my car says it will beat them. No SRT has yet wanted to line up against me in a drag race. I guess no one wants to be famous for being the first SRT to lose to a n/a V8. they prefer 80 punch where I have a slight disadvantage against modded SRT's. I think MB underrated the HP like they have done with other cars. My stock 500 engine has more torque than a SRT but what is really important is that a SRT does not have a very flat torque curve and reaches max torque at 4,500 rpm. the 500 engine reaches max torque at only 2,500 rpm and maintains a flat torque curve to around 5,000 where is drops off slowly. With the 500 engine you only have to change the engine and ECU. No need to change anything else. the 500 engine combined with the lower gearing of the n/a trans and 3.27 rear makes for a real beast. 500 engine are dirt cheap now but n/a 55's are becoming cheaper by the day. Just try to find one with reasonable mileage. The SRT6 engine swap would be the easiest, but even with this swap I would not change the rear end and trans. SRT owners have been wanting to run a 3.27 rear for a long time but can't without changing the TCU and trans. I saw Rudy this weekend and let him drive my car at the dragon. he mentioned that the car felt like it had the perfect HP for the dragon without being overkill. I encouraged him to build a lower cost conversion with the 500 engine. Shoot, Even Carroll Shelby sells GT500 and GT350's. There is a ton more cost in buyig a 55K engine, tans, ECU, TCU, 3.07 rear end and a ton more work installing everything which also includes heat exchangers, intercooler pump and plumbing and it takes longer because there is very little room to work in. There are big legitimate reason for the cost Rudy charges compared to what I did on my own. Basically all I did was take out one engine and bolt a new one in. but I LOVE the results.