The following write-up is an article S. Lucas Valdes (President & Resident Mechanical Engineer of GoWesty) wrote to provide some info on pop-top conversions.
"Hey, can I convert my hard-top Vanagon to a pop-top?" I get this question all the time. It is definitely tempting to go down this road since a hard-top version of a Vanagon or Eurovan is so much cheaper to buy than the same vehicle with the pop-top feature. Indeed, if you had two vehicles parked side by side, same year and condition, one with and one without a pop top, the one with the pop-top would easily be worth $5-10k more.
Anything is doable, including adding the pop-top feature to a hard-top. But let’s be clear: We are talking about a savings of $10k, tops. And adding a pop-top to a hard top is more work than meets the eye. It only makes sense if you have an otherwise un-restorable pop-top donor (crashed or rusty), the desire to do much of the work yourself, possess the tools, and have the time and talent—in other words, there is nothing easy about converting a hard-top Vanagon or Eurovan into a pop-top. If you are going to pay a professional to do it, you might as well just go out and buy a nice pop-top, since it will cost you a lot more than $5-10k to have one converted properly.
Another consideration is that once you are all done converting a hard-top to pop-top—even if it turned out perfectly and you saved some money—you still have a vehicle that needs to be gone through mechanically. The bottom line is this: it usually makes more sense to find a clean pop-top that does not need any major aesthetic restoration, even if it has high mileage. Then, spend your valuable time and money going through it mechanically. That way, you end up with a pop-top that actually runs well.
Those are my thoughts on the issue.