ET-3400 ROM adapter

In the last episode of the continuing saga of my little almost-complete ET-3400, you might remember that I found the LEDs for it, but not the ROM chip. Of course, it turns out the ROM chip is pure unobtanium: a special mask-programmed MCM6830A. Luckily, I found that Heathkit was still in business, and still supported the ET-3400, so I ordered a ROM chip from them. They send me a 2716. Hmm, it's not pin-compatible, so no big surprise that it doesn't work. So, I called them up. "Oh, you need an adapter board for that old ET-3400, but we stopped making those things 15 years ago." It turns out that one of the techs there has the last adaptor board sitting in his desk drawer. Now the adapter board is mine! But it needs a buffer chip. The tech says "I think it needs a 74LS174". But that's not a buffer chip, and it's got the wrong number of pins (16 instead of the 14 the socket has). I'm guessing it really needs something like a '242 or '243. Is there any way to know for sure without guessing? Am I going to blow anything up by trying the two chips above? Any other guesses? -- Doug