Yes stock 318 pushrod length is 7.5
Here is a simple test you can do to see if your stainless steel valve stems are sitting .030 to .050 ths too low.
Paint stick measuring 1 1/8" wide standing up off of valve cover gasket surface on the heads, your valve tips should be flush with the top edge of the sick to work with your stock push rods.
This picture is off stock 302 heads:
Have been measuring stock 318 / 360 valves for total length, they both come in at 5".
You badically have 360 valves in your 318 heads.
Think the main issue is your new valve seats were not machined as deep as the stock seats, coming up short on the valve stem tips.
Believe your new stainless valves are stock length from what I am gathering here.
My best guess right now you are at zero lash with no preload with your current setup.
Guessing you need to add .030 to .050 ths to the stock length of 7.5 push rod.
7.5 + .030 = 7.530
or 7.5 + .050 = 7.550 new push rod length.
Best to measure for new push rods though.