I think everyone wants you to succeed. I certainly am not hoping to see you fail. I don't think excuses about how difficult an engine swap is or that you're not a mechanic are legitimate. Fact of the matter is that there are a lot of people that bid on cars because they look cool but when it comes to the details, they don't know what they're looking at. I'm sorry to say that when it comes to builds like this, it's all in the details. Having a plan is critical and even then, things will come up, but how you deal with the details is critical. It is good that despite the deficiencies, you were very forthcoming with the photographs and that's great, but it's also important that potential buyers are aware of the issues with a car like this, as I'm sure you would prefer the (hopefully) winning bidder to know what he or she is buying and not to have to deal with the fallout of disappointment on the other end of the deal. I understand there are questions you can't answer or didn't realize would be questions.
There are lots of little issues that can certainly be addressed by the next owner, but the best path forward in keeping an S54 in this car is to really start over. The motor can certainly sit further back, the motor mounts are upside down and crooked, poorly supported, the M30 motor mount brackets aren't ideal, just as using the stock subframe engine mount locations (really, where the locating pin goes). The tabs that shift the anti-roll bar forward are now the anti-roll bar. You can hook up a 30mm bar and it will have no greater effect than those tabs can allow. The steering linkage with the bent drag link. I have nothing for that. The transmission is a Getrag G250, which fails regularly behind the 2.5L M5x-powered cars they were supplied with. I can't imagine how long that will last behind an S54. It's certainly cute and can fit in your pocket, but its not a strong one. On top of that you're limited with small clutches. The crossmember is putting a lot of weird pressure on the transmission mounts. Add to that the small guibo, that's a fuse that will keep blowing. Also, crucially, the diff mount - a known weak point in these chassis - hasn't been reinforced. I don't know why so much trouble was had with the fuel filter/regulator placement. The white S54 car had it above the right rear axle. Much safer there, much less vulnerable. Surely, it's more plumbing. With some noodling and a complete rethink of the exhaust, the car will make a good deal more power than it does currently. Right now, it's being strangled just looking at how the header "collectors" are routed and the pipe sizes and the multiple 90º bends. I don't think you'll like the results on a dyno.
I think there are some positive aspects definitely. Lots of custom touches like with the gauges, the interior is quite nicely done. Its a huge improvement over the previous listing. The seatbelts seem incredibly dangerous with those bolts (are the belts from an E24?), but other than that, it's probably the best part of the car.
I could nitpick on a lot of things, but guess what? You can nitpick every car. Nothing is perfect. You know the car isn't perfect. That's fine. There are some fundamental issues with the engine swap and they're not easily corrected. I am not trying to be mean or piling on, this is just what I and others are seeing. I'm putting this here on the forum and not on BaT. I certainly wouldn't go around saying the car has 400hp. I don't see that ending well. I wish you and the car luck in finding an owner that is willing to make the commitment to improving what you started.