Yup - I'm waiting to get some finishing on it before I do too much with it - it's just hard to build something and not at least fire it up!
As far as hight, the interior is 21 7/16 tall - but you could build the access panel to fit just about any 18" driver. Right now, I have to tilt the driver to get it through - but I made mine a bit smaller than "them".
According to the plans, their access panel actually extends over the baffle plates by about 1/8" - 1/4". I did this at first, but had to scrap that build and start over. I think they have a CNC that layers their access panel so that although the back dimension is wider than the "allowed" amount, the inner dimension is probably 3-5cm smaller.
Either way, you could load any driver - but I made this door just big enough for the 18PZB100 - not sure how a different driver would work though.