Make sure all battery connections are clean and tight. The battery ground connection must go to the engine block and have a clean connection to bare metal.
The starter recieves it's ground connection through the engine block. The starter and block must be bare metal to bare metal there.
The starter solenoid must be in good condition internally. If the internal contacts are worn the starter will not get full power.
The starter brushes must be in good condition. They can be examined by removing the end cover from the starter. If the brushes wear down to the screws, it will drag and increase starter load enough to lower ignition coil voltage and prevent starting. The starter wil really jump and jerk, sometimes stick and needs to be struck with a hammer to get it going again with bad brushes. The interior dome light will almost go out during cranking if there is a really high amp draw of the starter, indicating a connection problem or internal starter shorting.
If the starter armature bushings are worn, the armature move enough to drag on the magnets and starter amp draw will increase.
When hot, try a jumper or remote starter button on the purple wire of the starter to battery +. MAKE SURE THE CAR IS OUT OF GEAR!
If there is no problem starting this way but there is a problem with the key starting it. You could have a bad neutral safety switch or if you have a 69 Camaro with transmission lockout switch, that uses the same switch on the steering column as the automatics use for neutral safety. This switch or the ignition switch can have the contacts inside burn, wear, or pit and the added resistance can sometimes prevent hot starting or the starter will only make a slight click.
If your starter is turning the engine but not turning it very fast, I'd suspect internal starter drag, worn brushes, bad connections-grounds, poor battery output, maybe a failing alternator is not charging the battery enough.
Many people will tell you to add a Ford type remote starter solenoid to your car. It will help cover up a bad ignition switch or other wiring deficiency in your car's wiring, if that is your problem.
I have usually solved it without going that far.
I like the standard motor products solenoid, Part # SS200. It is more heat resistant.
Weaker GM solenoid return springs are available for heat soak starter problems too.
Starters for low performance engines don't turn over high perf engines very well if at all. Make sure to use a Z/28 or Corvette engine starter for the "special high performance" engine.
All big block starters are ideal as they are all high torque starters. Just make sure the starter fits your flywheel size. usually staggered bolts on the starter are for large flywheel, in line bolts are for small flywheel.
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer