Well since my last post inquiring about VM heads I've stripped mine down (on the cheap, as pictured below). I came up with a real ad hoc pressure test setup to verify exactly where #1 was leaking to have filled that jug so much. Consists of some angle Alu, A bicycle inner tube and some of the coolant gallery bolts. Filled the head 2/3 full of water and pressurised them to about 35 PSI. Boy did the bastard leak! It came out from the bridge (Insert?) between the valve seats. Toast.
https://imgur.com/a/VlhaJv0
https://imgur.com/a/Ll4tOgn
Took all 4 heads to a local shop and they tested them for hardness. They rang in at:
#1 - 65 HRB
#2 - 67 HRB
#3 - 66 HRB
#4 - 88 HRB
All pretty soft and it shows... The liners have grooved into the heads enough to make a bit of a burr. Guy at the shop was great and said he wouldn't even consider taking my money to test em because they're too soft to be reused anyways. It would just lead me straight into more gasket failures. I've read about quite a few people changing head gaskets on VM's, finding the heads to be "good" and eventually getting terribly short life out of the new gaskets. This could be why?