If 4" is a higher popup that means you probably have 2" popups. I don't know about where you are but 2" heads aren't ever used on lawns around here. It's just not tall enough for 2" or higher grass. There is virtually no difference in price between 2" and 4" hunter bodies. Any idea why 2" was used? You're only talking about $75 bucks for replacement bodies but depending on how much irrigation installers charge in your area, you could be looking at a bill of around $1,000 or more and that's just for replacing the heads. It could need more than that. I think your best bet is to do as bpgreen recommends and lower your deck but if the system was put in recently and the installer saw you mowed your lawn at 2" then you might want to contact them and see if you could work something out.

Two trips to the local Ace hardware and I was able to find a replacement sprayer head. I sure hope this one doesn't go missing too.

It is a huge design fail to mix irrigation types for the same zone. If your rotors/sprays have output adjustment (ie change nozzles, spray heads) you can mitigate the effects, but it's still a bad idea.

without digging up the head to be sure how it's mounted i'm going to assume it's on a fixed riser so changing to a 4'' may be a problem. if it's on flex pipe installing a 4'' is no trouble. if you don't feel like digging up the head try calling around to any sprinkler supply stores in you area and ask for a 2'' pop-up head and someone will have or can find what you need.