Hondata has base maps.
Good luck with 300hp out of a Greddy/Mitsu turbo on a Honda. You'd find MUCH better results on a t3/t4 50 trim.

I couldn't find any hard evidence, but I believe the 18g only supports about 300hp anyhow. Maxing that thing out on stock sleeves would be deadly. You said your fully built, I assume that includes sleeves. So it's attainable with 550(Would 450's get maxed out?)'s and an Ungodly amount of tuning... Your just going to be looking at 18psi+ when you could get similar spool and more power out of a 50 trim with less boost.