Update:

I was using the wrong search terms. If anyone else is interested, service manual for 67 and 68 birds:

http://thefirstgensite.com/html/P67svcmanual.htm

http://thefirstgensite.com/html/68smi.html

I think I've figured out why my motor ran like garbage. I was told it was rebuilt (I took that with a grain of salt) but apparently it really was... but back in like 1994, not recently.

So I ran a compression test. Good compression in 2 cylinders, like 80 PSI in a 3rd and +/-30 PSI in 3. No wonder it ran like crap. I was highly considering pulling it and selling it because of the cost of parts, etc, but I put my borescope camera down the cylinders and they looked brand new... hmmmmm. Adding oil did nothing to help compression, so probably not a bottom end issue. So something in the valve train/head. Pulled the cam housing and the head. I found that 2 lifters were stuck in their bore and one lifter was broken. IN ADDITION to that EVERY SINGLE hydraulic lifter was STUCK in whatever their last run position was probably 20+ years ago. And I mean stuck good, like I had to pinch it in my bench vise to get them to pop and even after that they were still pretty sticky. Ordered 12 new lifters from Kantor and they move free/easy.

The intake valves were also pretty sticky. I cleaned all the valves, lapped them, and I'm currently waiting on my seal kit to reassemble. I have high hopes this engine is going to run really well.

Cylinders 2 and 3 look almost like they've never fired since the rebuild. My dad and I think the motor was rebuilt in 1994, either something happened, or the car just sat, but it basically hasn't been run since then. The guy I bought it from probably thought he could just do some stuff with plugs and timing and get it going, he couldn't, so he kicked it down the road to me.