Heathkit ETA-3400 vs. ETW-3400 confusion?

Which is the correct model number for the I/O & memory accessory for the Heath ET-3400(A) trainers? I see ETA-3400 and ETW-3400 used interchangeably. For instance, the d/l manuals refer to the unit as ETA-3400 but many (most?) units, mine included, are screened ETW-3400 on the case. Anyone know what gives with this? Are there actually two different models or revisions, as with the ET-3400 and ET-3400A? Also, is there a way to tell if a Heath piece is factory-built? My recently-acquired ETW/A-3400 has a board which almost +must+ have been wave soldered and washed. It has no traces of home-assembly. Likewise, the rest of the build is top-notch and looks like factory work.. Thoughts? PS Still need a 2x20 header (like 40pin IDE) to complete this project. Anybody got a spare?