As mentioned before, on the Athearn and other plastic SD40-2s, the intake fins are solid. To fix this, you can do what Liz did on her outstanding SD45X project (Harry Wong photos of it here: http://www.pbase.com/tracktime/sd45x_elizabeth_allen ), and use modified Cannon SD50/60/70/75 dynamic brake intake parts, cutting them up to get the proper style for 2nd Generation EMD hood units. While this is certainly a doable (and great looking) option, I decided to take a different route. I raided my parts stash, coming up with the intake pieces from an Athearn SD45-2/T-2 parts sprue. On these units, the sides of the dynamic brake housings are tooled as separate parts, allowing for finely detailed, see-through intake fins.

An unmodified SD45-2 d/b housing can be seen at the bottom of the pic, with a modified one immediately above it. It was cut-down using an Xacto saw in my mitre box to match the length of the opening I cut into the Athearn SD40-2 dynamic. Heightwise, it's a bit tall (by roughly .015", give or take a thousandth), but that's nothing a few passes in my True-Sander can't fix. That is, as soon as I can find the guide assembly for it.:-/ Once that's out of the way, I can build a backing plate to accommodate resistor grids to mount behind the intakes. And yes, only one side has been cut out of the SD40-2 housing so far.:)