I know exactly what I would do with that car.
1. You already mini tubbed one side. Don't undo it. Just do the other side. So what if you decide not to run extra big tires? You still have the OPTION any time you want.
2. I agree, I would go with a traditional LOOKING small block (well almost). The old SBC platform still performs pretty darn good with a good hydraulic roller cam and some AFR heads. You can get essentially big block performance (with apologies to Freddie, whose car BTW is one of my favorites) with 400 + cubes and some AFR heads. These can easily get you in excess of 500 HP and still be streetable.
3. Agree with Freddie on the 12 bolt.
4. Forget about the four speed. Use a good 5 speed with OD 5th gear. You can get a shifter that will come up in the stock location, so you can't even tell by looking. You can run either a 3.73 or 4.10 rear with a .66 OD and still cruise on the highway. Best of both worlds.
5. I would paint the exterior to look bone stock including the white pin stripe. Great look on the 67.
6. Bone stock interior. They are handsome, and cheap to do.
7. Install subframe connectors and traction bars. I would not mess with a cage, unless you are going to need it for the strip. If so, go minimalist; maybe just a vintage 3 point.
8. I too, love the 15 inch wheels. On my 69 Z I runn 255 60 R15 in the back, and 215 70 R15 on the front. No rubbing issues. See picture below. Mine is the black one.
9. You can spend a ton on bigger brakes. If you like tinkering and want some kick ass brakes cheap, do what I did on my 68 El Camino. It was a 307 PG car with four wheel manual drum brakes. I bought a booster and MC from a guy who was upgrading his Disc Drum set up to four wheel discs. $60. I then sourced all the parts I needed from Rock Auto (other than caliper brackets which you will need to source... but it can be done) and used 77 Chevy pick up calipers, C3 Corvette rotors up front (which are ALMOST 12 inches, but fit nicely inside the 15 inch rims). See my odyssy here:
https://www.camaros.net/forums/16-br...e-upgrade.html
A member here GAVE me some old backing plates off of a full size car and I put 11 inch drums on the rear. That El Camino stops amazingly well.... even with a trailer when the trailer brakes don't work... and sometimes they don't. I don't remember the final tally, but it was much cheaper than a kit, and I had fun doing it. The procedure would be the same for you 67 Camaro.
10. I wouldn't spend a ton on suspension. Do the Gulstrand mod on the upper control arms. Rebuild all the suspension pieces with Moog parts or delrin. Personally, I would go Moog. Get a set of big block springs for the front and cut off on coil. Install a good set of leaf springs on the rear that are a bit stiffer than stock. If you decide to go HUGE on sway bars, I have a rear bar you can have for free if you will pay shipping from Oklahoma. I took it off a friend's car that still had the stock 11/16 bar in the front and some knucklehead put a giant (I THINK it is a 1 inch rear bar, but may be 7/8.... would have to measure). This will not be a world beater, but will be so much fun to drive; and a lot less headache that trying to make a full blown pro touring car that will barely handle better than a new Hyundai.
11. I would install power steering. Plenty of write ups on PS boxes. I used a WS6 box on my car at one time (has the original manual steering on it right now) and had hoses made. Lock to lock steering was about half of stock, and it had great road feel. There are kits if you don't want to piece things together.
12. If I lived in San Jose, I would probably not put AC on this car. However, I live in OK, where we regularly top 100 in the summer months. One thing I don't like about my Z/28 is lack of AC. I rarely drive it in the summer. Black car, black interior. Butt blisters waiting to happen. If I were to build a 67 or 68 I would go with Vintage air with a Sanden compressor.
13. I would not go overboard, but would put one of the decent retro sound systems in. Keep it looking stock, except for some speakers.
You can tell I have never thought about building a 67 or 68. Like Freddie, I would LOVE to build a 68 to the above specs. In fact, if I ran across a great body minus engine and trans, I would be tempted, as I have the TKO 600 and a 427 small block just waiting for some AFR heads. My problem is all the cars I have lined up in front of that one. But, if the right deal came along on a cherry 68 body, I would really be tempted to shuffle some things.
Whatever you do, pick a plan and stick with it. Minor changes are no big deal, but stick to the plan once you commit to it. Work will progress much more quickly and smoothly, as you won't be frozen with analysis paralysis on a regular basis.
Good luck. We will need to see pics of your progress.