I've been researching this topic and I think I've come to conclusion that won't be going this route.

I could install the bucket/racing seat and use the OEM seat belt with certain modifications but the seat belt would not work as effectively. The high side leg bolster would create too large of a gap between the lap belt and the pelvis. The belt should be firmly against the pelvis to hold in into the seat. Even if you are able to feed the buckle through the opening at the side bolster, the shoulder strap would run into a similar problem with the side shoulder bolster. The three point seat belt is designed to work with a seat that is not a fixed bucket. I contacted Buddy Club and they told me that I could use the OEM seat belt with the seat but I would need to relocate the buckle to the seat side rail. The issue with the gap between the seat belt and the body remains however.

The next option would be to use the Takata Drift II 4-point harness that I already own. I was looking into how I would install this and how it would work. The harness is designed to keep the torso firmly planted in the seat at the level of the shoulders and the waist. However, in circumstances where the inertia from an impact wants to throw the body foreard, the torso doesn't move but the head does. Unless you're using a HANS device or a neck roll, your head will be thrown forward with significant force and forward flexion of the neck causing vertebral injury, spinal cord injury or significant brain injury. You shouldn't use it for street driving because of this.

The other thing that can happen unless the harness is designed to prevent it, like the Drift II is, is a phenomenon called "submarining". Some people believe that it's what happens when you slip under the harness and fall into the foot well. In actual fact, what happens is that the shoulder harness pulls the waist harness upward into the abdomen rather than keeping it at the pelvic bones. This can lead to significant internal organ damage. The other thing that can happen is the harness can forcefully pull the torso down into the seat creating an axial load leading to compression fractures of the vertebral bodies.

I also contacted Takata to inquire as to how I would install the harness if I decided to use it. Since I have a del Sol with only two front seats and no rear seats to use the rear seat belts to fix the harness to as an option, I was advised that I would need to install a roll bar or roll cage. This is another dangerous modification. A roll bar to fix the harness to can and will warp and fail. A bar failure will result in the harness failing to keep the occupant fixed to their seat. The bar can impact the driver's head or the driver's head can impact the bar. Unless you're always wearing a helmet, this is a very dangerous and potentially life threatening situation. The same goes for a roll cage. Serious injury or death can occur if the head or neck hits the bar or cage.

So what I've learned is that a bucket seat and harness are not suitable for a vehicle that will also be driven on the street. An OEM seat belt doesn't work well with a fixed bucket. The only time it makes sense to install a roll bar or cage is when you install the safety equipment as a whole system. Bucket, harness, HANS, cage/bar.

I think I'll end up returning the harness and opt for a seat option that allows for movement of the upper torso portion and use of the OEM seat belts.