Walk away from that. You have to completely disassemble a transmission to remove "just one gear." There are tons of unmolested 6-speeds sitting in junk yards across the country, go find a low mileage one.
Just walk away... you will get what you pay for.just got a reply from the seller and he said he only changed the reverse gear as it was making a wining noise when reversing. he also told me that later he found out that, if he used better transmission oil (MT-90) the noise would of gone.
anyway he suggested that he will put his original reverse gear back in and give me a hand on replacing the whole box. seems like a nice chap and 6 speed box is only $250