Vollmer conversions are pretty hard to beat. I have two HKs that have been through Vollmers shop -- both are Billistics conversions, but had been reworked and finished in their superb finish (one SuperPlate, one the predecessor to SP). The thing I dig about Vollmer is that you pretty much are going to get (or better) what he describes. I also picked up a converted AR15 from them -- while the finish is somewhat lacking (but I knew that up front), the function is 100%.
IMHO, you really can't go wrong with Vollmer products. True, the price is a bit high (but on HKs, it's pretty much that anywhere!), but you will get it as described and it will work.