Why stop at y73? Wouldn't it make more sense to go all the way up?
Because that would keep most of the system hidden underground and all you'd see from ground level would be a small factory. You could, of course, increase the height by a ton.
The way I personally do levels is 8n+1 for the y value. What this does is factor in your max upward reach. While on foot position 1, if you mine straight up and then stand on the block you can't reach you'll be at foot position 9, so your levels would be multiples of 8+1 for where your foot position is. The way this works out is you have 7 blocks of air and the 8th block is the ceiling. Due to this lay out you can make each level two floors per level with a height of 3 per floor.
Yea, I know, that probably came across all weird, but that's how I do my mining and whatnot (though I personally prefer a 4-2 split for floors so I have the main floor that's 4 high with a 2 high space to hide the wiring for my machines).
I know you didn't ask all of that, but it's a way to factor how many sets of 3x3 ovens you can place in a chunk. Each level can contain 32 ovens (each level consists of 2 floors). Then reverse the 8n+1 equation where 8n+1=256 (for max build height). Then 8n=255 which comes out to 31.875, or only 31 levels where you can place full coke ovens. There's two floors per level so 62 floors, each floor holds 16 ovens so 62x16 = 992. So if you have flat bedrock and build to the max possible height limit you can fit 992 coke ovens in a single chunk, but then you'd have a massive square tower going on forever.
tl;dr If you did build to max height you'd get 992 coke ovens into one chunk with flat bedrock.