Check with Bill at Mile High Performance, he seems to be able to source unobtainium parts for Land Cruiser engines. Another option is to sleeve the cylinders so they can accept stock sized pistons. Gunn should have known better though!
BTW, I know of a few people who have used F heads on 2F blocks to get better compression. The only gotcha is having to oil the rockers, which is just some extra work. If you want to go that route I have a good F head you can have for free.