This is a bit of a sore point among M35 owners.
Both Bis-e-bee & Jetwreck spent good money and a large amount of time procuring spare ECU's, and were given various assurances about the ability to re-flash their ECU's. After a huge amount of running around on their part, I believe Jetwreck's ECU has now disappeared, presumably, never to return. So he is out of pocket and no closer to the promised solution.
It CAN be done; (Nismo, G-zone, Impul and one other do it) but no-one in Australia can do it (others know more of the technical issues than I do) apparently it is quite reistant to changes.
There is no shortage of demand now, but most have given up hope of a reflash. Personally, I'm not really after much extra power, but I'd give my left nut for a linear, direct action throttle and slightly better fuel economy.
If you feel like throwing your hat into the ring go for it!
BTW wht510, I sat down & read your entire 1600 build thread the other night; Brilliant, just brilliant .