Uh? What I'm selling IS a complete CvS2 for a JAMMA cab, but you can re-write the card to MvC2...
The "problem" of you needing a JVS power supply will exist no matter what Naomi+DIMM solution you put in your cab.
Net, GD, CF, it all requires more power than a Capcom IO can supply from JAMMA harness.
Disregard if your talking about cart only, a MvC2 cart WILL boot with just a Capcom IO.
The error 21 happens occasionally, it seems to be a issue of the DIMM board needing to be positioned just right.
Honestly all Naomi hardware is a little flaky in this respect.
Again if you are looking to run a DIMM based Naomi you're also going to need a JVS power supply.
A DIMM is a reprogrammable cart that loads data from Network or GDROM/CF upon power up, they draw more juice than a normal game cart.
NetDIMM (loads games via network)
GD-ROM (attaches to GD-R DIMM not pictured but looks almost the same as above)
CF Kit (same as GDR but replaces disc drive with CF card)