Actually most of those numbers are off, as they should be ranges and not hard set numbers. This is where everyone goes off the rails with numbers. If everyone kept a tank with the same numbers, then we would all be successful, right? But that's not how it works. The only parameter that should be targeted is salinity and it should be 35ppt. This is the baseline for all natural reefs and what we're trying to copy in our tanks. Most, if not all test kits are based around salinity of 35ppt.
Temp can be 76 - 80 with the target in the middle.
Ca can be 380ish to 450+
Mag can be 1280ish to 1500
Alk should be 7 - 9
N & P should be measurable. NO3 >1ppm and PO4 >0.05
I think if you're keeping N 10x of P, then that's a good starting point and you'll find the range that best suits your tank and animals. Again, don't go nuts on the numbers, let the animals tell you what they're happy with.
But the most important thing with keeping clams, is light, light, light. If you don't have the quality and quantity of light, then all of those numbers listed above are worthless. Light is the number one parameter that needs to be addressed with keeping clams. Once you have that nailed down, the rest of this will be easy to follow and manage.