Building a smarter air compressor-- my Champion Project compressor

[oil pan 4]

That's a clever approach but I'm pretty sure, not readily done on the R15b, I think it's more common on even larger pumps that generally need a least 7.5hp.

If there's no intercooling between the stages that seems like it would lose a lot of the advantages in efficiency that a 2 stage would offer. Assuming you need to have well above 100psi.
For me more tank capacity and more single stage compressors does the job.