Finally I got my Stack-Up NES cartridge from eBay. And yes, there’s almost 100% chance that in these cartridges are Famicom converters inside. When Nintendo released Stack-Up and Gyromite for America, they were in hurry to sell american systems, so they didn’t manufactered independently NES cartridges, and put these 60 to 72 pin converters inside the NES cartridges. Some other games had these converters too, but the chance to find one is smaller than in Stack-Up cartridges.
What you see on the left side is my finished homemade Famicom to Nes converter with the Ballon Fight Famicom cartridge inside. To protect the rom chip from dust and other things, I sticked a white plastic sleeve over the black converter. And without messing up my NES slot I put 2 solid cords on the left and right side, which are connected on the black converter. With them you can better take off the cartridge from the NES slot. A similar method, a strip holder was installed on the rare and now expensive Honey Bee adapter, which was a black market Famicom to NES converter released in China. You can still find Honey Bee adapters on eBay, but they are very expensive. The Stack-Up game I took off from the converter (sorry for destroying the case), pictured on top of the right side, I still can use on my Neofami console. I just have to put it in an empty Famicom cartridge and buy a Family Computer Robot or R.O.B. for NES, but that’ll be another exciting story.