Very interesting, I've been wanting a RAM cart for my SD1 for years until I found a genuine RAM cart online (Stor-Cart 32) - but now as this PCB exisits I could be interested if the PCB is available for purchase which is where all the time and effort goes. Just a word of caution, there cart PCB for the ESQ1 looks the same except the two are different, the ESQ1 takes a 64k chip and as you say this VFX/SD is the 256k device.