I'm a little late to the party but figured I'd post my thoughts if only for documentation purposes.
Despite 'safety' and '510' being somewhat of an oxymoron, this is a topic which has gone through my head many times - and literally every time I'm behind the wheel of my 510. I always remind my son that the 510 is a 4-wheeled motorcycle. Assume you're seen as such and the result of any accident would likely be comparable...
I'll break my safety approach into 2 categories: setup & driving, and point-of-no-return structural.
Setup/driving is obviously the most important component, and is a broad subject. To me the two most critical elements are 1) to have a machine that allows you to react first, and 2) putting yourself in situations YOU can control.
Setup: Nimble chassis (complemented with tight suspension and steering and wheels/tires) and strong brakes are your weapons of defense. Learn how to use it!!! For those who haven't autocrossed, get out there and see what the car can do in a safe & controlled fashion. Repeat your outings until it starts to become a subconscious competence skillset. If you have to think about reacting, or first wonder what the limit of the car is before executing a maneuver, it's often too late.
Controlling your environment through driving habits: Defensive driving doesn't mean slow! In fact I typically avoid those cars plastered with 'War-Amp' stickers knowing they are often an issue. I often like to carry speed because it's a whole lot easier to scrub speed off than trying to gain. Speed (bear in mind this is in reasonable context, not 50kph over the limit) gives you one more variable at your disposal. I also like to be in constant awareness of my environment (where cars are located) and my position relative to them. I don't like having a car hovering off my quarter panels and thereby closing a potential exit/avoidance maneuver, nor to I like to have tailgaters (catless exhaust does help that quite a bit though ). If I'm in any of these situations, I take advantage of the car's power (and gain speed) to place my car in a better environment. Finally, assume that nobody sees you! Seriously, drive like you're invisible and you'll likely avoid 95% of dangerous situations.
Short of a cage/racing seat/harness, if you're at this point odds are whatever changes you've made to the car will make little difference to the final outcome. Still, if every 1% counts why not?
Front collision: Make sure your crash structure is in good condition. Mine was quite rotten and needed repair.
While you're there why not a bit reinforcement with bracing?
Besides that IMO you're next concern is smashing your face into the steering wheel. Either get a good modern seatbelt system and position yourself so that the inertia reel can react quickly enough and the slack in the belt is consumed BEFORE your head touches the steering wheel, or more ideally but less 'user friendly' is to install a more static fixed fit belt system like a 3 or 4 point (Schroth Rallye 3 fastened to the rear shoulder mount on the C pillar has tempted me).
Rear collision: Besides making sure the basic structure is sound there are a few options to consider. I have a bike mount installed inside my trunk (swinging licence plate allows the rack to come inside the trunk to mount). The added benefit of this setup is that it's acts as a secondary 'bumper' in case of a severe rear collision. Both frame rails are connected (cupped with a large 'U' bracket underneath). I'm thinking of adding another bar to go just above the receiver to effectively raise the bumper height, and add another bracing to the rear wheel well.
Besides that, a good seat with proper neck support should be sourced. In my case I used seats from a 260Z.
The battery (if in the trunk) should have careful consideration where it's placed as should the cables running to the engine bay. I would also consider adding a metal fire barrier to the back of the rear seat bracing and speaker holes - as I discovered a couple of years ago when there was a fire in my trunk and flaming up through the rear parcel shelf with my 9 y/o son in the back seat.
Side collision: Not much one can do there I'm afraid. Sure you can add a bar, but there's soooo little room from the outer door skin to your thigh you might risk it intruding into the cabin and being a source of injury. Even if it did help, I can't imagine your head would fare too well hitting the B pillar/glass/grill of that Dodge Ram. Thankfully that's one of the more rare tyes of accidents *IF* you drive in a manner that nobody sees you.
Unfortunately it's a bit of a balancing act of adding weight through structural safety that ultimately compromises a characteristic of what makes these cars so fun to drive, light & nimble. You could go as far as adding a full cage (offset rearward enough that you don't hit a bar with a helmetless-head) or implement some of the suggestions I have/will do.
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