This is the tool I use and it goes very fast cause you do 2 springs at once. The Thunder Racing tool looks nice also. It should work fine in a Corvette, but looks like it would be a bear to use on an F body under the cowl.
Seals go to a local autoparts store and find one that carries Victor Reinz/Dana engine gaskets. You want part # B45919. They usually come in packages of 8. If you can’t find them locally I have them in stock.
You shouldn’t have to worry if each cylinder is at TDC. Just make sure your car is in a high gear like 5th or 6th and have the wheels chocked so the car doesn’t move on you when you hook up 90-100psi of air pressure
You can reuse retainers and locks. If you are using a different valve spring make sure the installed height is the same or to spec for that valve spring
That Victor Reinz part number I gave you are high temp viton exhaust valve seals. Use them on both the intake and exhaust. They are brown in color instead of the standard black rubber