Depending on how much lift you want and the arch/ride height of the springs all of this may be moot. The rear shackle mount sleeve may be mounted to the BOTTOM of or frenched into the frame instead of running through it. Jeepers have been "outboarding" springs and shocks for decades. There are numerous companies that make kits expressly for this purpose. There are also several straight axle swap kits that come with all the stuff needed for this swap using leaf as well as coils. As with anything like this, your fab skills can determine if you have to spend $1K or $5K on this type of DIY undertaking (or $10K+ and just dropping it at a shop and not getting dirty). There is nothing wrong with any of these methods so long as the end product is safe and meets your needs. Don't fall into the macho "built not bought" BS. Do what you need to and get the vehicle you want. If I had the need and the circumstances I'd have no reservations about ordering a new Sportsmobile that I could fully finance and get a regular factory warranty on. The chunk of money required to have a conversion performed on an older van, that must be paid all at once, can definitely steer someone to one choice over another.
Honestly springs are cheap in the grand scheme of a project like this. Depending on your build experience, building a bastard pack by mixing and matching junkyard springs from different packs would allow you to tailor them to your needs/wants. If you aren't confident in your abilities or quality of the used spring packs you could then take them to a spring shop to be replicated with all new stuff. That would get you as close to perfect on the first try, resulting in less down time and cost. Also if you have any wheeling buddies in your area you can probably recoup most of your jy spring costs, or keep them to use for another project down the road (pun).