Check the area under the battery socket by the RAM and above the battery by the power switch; there are two of those @#&*$#@!! Leaky caps there. Check to see if they leaked and replaced them anyways! They leaked on my IIfx and I'm waiting on on a couple of caps to come in by mail. They are 47µf @ 16V.

Otherwise it looks clean! Congrats! Did you take out the video and ethernet cards?

You'll need new PRAM batteries on the mother board to turn on the IIfx. Or it can be jumped started by sending 3.5V through I believe pin 15 of the PSU's connector on the mother board.