Hi Chester,
I don’t think I would call this a mistake. The quality and performance of blended Dunlop is not as good as all natural Dunlop but it is still a high quality material and better than many other types of foam and it can be good value for budgets that are lower. It certainly won’t “foul anything up”
The choice beween Talalay and Dunlop would be based on personal preference depending on which different “feel” you preferred. There would be no better or worse here IMO.
I also probably wouldn’t go with a flippable mattress for a truck and you are getting into a more complex construction with this that I would take on with a DIY construction (there are complicating factors involved with a two sided mattress) but you could certainly use a 6" core and a separate topper that each that had their own cover and then each of them could be flipped this way.
I would think that you would likely do best with a comfort layer of 28 ILD or above and I would tend to go with Option #1 but any personal testing you have done on latex would provide a better reference point. Once you have this combination … then you could decide what if anything else you would need to add.
I would b hesitant to make an ebay purchase from someone i wasn’t sure was selling what they listed but there is a list of some good DIY suppliers in post #4 here and one of them is an ebay supplier that sells seconds that has a confirmed source and describes their product accurately. You can also see a review with pictures in post #6 here.
Phoenix