Heathkit ETA-3400 vs. ETW-3400 confusion?

[drlegendre .]

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?