Apparently life and work had other plans for my time, so it took far longer to get around to testing and then posting about some working boards. And my Rigol went bang, so I was a little sad. Excuses out of the way:

Testing was done with a PicoGUS SB16+Waveblaster(GM MIDI) in Doom and Duke3D(D1/H1) and the same games with SB16 PnP+Adlib(D1/H5), Unisound init.

ASUS P8Z77-M - LDRQ1 is available on an unpopulated resister pad next to the chipset heatsink. Confirmed working with PicoGUS and SB PnP(CT2970). No debug/80 codes. IRQ5 cannot be freed up.

ASUS P97I-PLUS - LDRQ1 is available on an unpopulated resister pad on the back of the board. Confirmed working with PicoGUS but *not* SB PnP. Debug/80 codes work. IRQ5 cannot be freed up.

Gigabyte GA-Z97M-D3H - LDRQ1 is available on an unpopulated resister pad under the chipset heatsink, that is also via'd to the back of the board. Confirmed working with PicoGUS and SB PnP(CT2970). including on IRQ5(!) for SB. No debug/80 codes.

Asrock X99E-ITX/ac - LDRQ1 is available on an unpopulated resister pad on the back of the board. Confirmed working with PicoGUS and SB PnP(CT2970). Debug/80 codes work. IRQ5 cannot be freed up.

Kontron 886LCD-m/ITX - LDRQ1 is on the LPC header, LRESET is missing. PCIRST on this board is 3.3V high and connected to the Winbond SuperIO as well which, according to the docs, expects 3.3V TTL on LRESET. So, borrowed PCIRST. And....it works. Without config and an SB16 PnP even shows up in the BIOS summary screen:

PicoGUS, SB16 PnP work fine, BIOS lets you reserve IRQ 5/7 as well.

sapphisa/lpcisa see the LPC controller but not the bridge. Reading the 6300ESB docs I get the impression the LPC controller uses 4E/4F itself, and maybe also 2E/2F. But once I've assembled my final dISAppointment I'll try populate R6 and retest with 2E, unless someone smarter at reading chipset docs than me says "no". I may also stick a zener trimmer on the PCIRST wire out of an abundance of caution, although I don't think there is a practical way for it to go 5V.

Still to test:

VIA VB6002 - VIA chipset, so either it does the Kontron or I'm going to have to delve into coreboot code
ASUS/Pegatron IMIR-VM - TPM header but LDRQ is not on the pinout, no boardviews, and GPIO23 toggling + scope probing has been unsuccessful so far. They're cheap enough that I might just buy another, hot air the chipset off and copper broom it. But this is more of a curiousity and limit test to see what kind of early boards can be made to work.

I'll do followup individual posts of each of the above working boards over the next day or so.

Can't edit my post(due to post count I assume), so quote clarifications.

tecpossum wrote on 28 minutes ago:

ASUS P97I-PLUS -... but *not* SB PnP.

SB PnP is not detected, so I'm guessing like some other ASUS boards in this thread PnP IO ranges is blocked/dead.

VIA VB6002 - VIA chipset, so either it does the Kontron or I'm going to have to delve into coreboot code

JLPC header has everything on it, but my board needs to be recapped before I go poking at it more. So might be a bit.