Your box may be blown...Jack will know where to look/test. Too lean sounds like.

So some good news this morning, I took a stab at adjusting the mixture last night and it's now running much better. I may still fatten it up a bit more for now, rather be on the rich side than lean. Still planning on taking it to Jack's to really get it dialed in and hopefully have him give it a good once-over.
Fortunately between the improvement last night and the smoke test from earlier I feel fairly confident the airbox survived, but I'll have him inspect just to be certain.

Thanks for the help everyone!

And I definitely agree on the importance of AFR gauge, especially after seeing the difference in just a small adjustment.. I'll be installing one ASAP

Don’t forget to check/adjust ignition timing. CIS will compensate for elevation change, however the ignition timing will not. Fuel mixture and ignition timing go hand in hand, especially when dealing with elevation as oxygen density varies.

Good deal...I had some pre AFR backfires that I/we survived... the pop off did its job and put a dent in the wire mesh filter screen but saved the box. Some guys hate the pop off and say it can lead to an air leak...perhaps...I love mine as it saved the box a few times.
I put a thin coat of silicone paste on the rubber seal, the same stuff I use on my pool rubber seals. Keeps it pliable and well sealed.

I second Josh's comment.... do you have a Bently's 911 SC workshop book? If not get one. You can check the maint. write ups on this site for a quick timing tutorial.

Not yet, but it's at the top of my list.

So I've got an AFR gauge on the way from another forum member, and I'll get the timing dialed in tomorrow. Should be running strong after this weekend, thanks again guys!

When you get the gauge feel free to ask any questions about the install. Say hi to Jack for me...Pat from Wickenburg, he is a great guy btw. and actually talks you out of spending money and doing work that is not needed. Unusual for the biz.