Ne-330 was planned as improved one but not in time for the end of war.
Not to be nitpicking, but Ne-330 engine was in construction twice before the war ended. The first finished in April, but bombed on the day of the trial run (April 7). The second never. Maybe that is what you mean and I misunderstand (sorry if so).
Reference:
「
日本陸軍試作機大鑑」
by Minoru Akimoto, 2008.
「
三菱重工業株式会社史」
by Mitsubishi Heavy Industries, Ltd. Company History Editor Office, 1956.
I've heard there were three engines planned for use: the Ne-12 (which was applied), the Ne-20 (also applied) and the Ne-330 (incomplete).
Ne-12 is an early planned engine, but only Ne-20 was ever mounted to Kikka in reality. Ne-330 is far too large for the Kikka frame, the engine developed for planned Kikka types (namely, interceptor) is Ne-20 Kai, an improvement of Ne-20 with a planned thrust of 650kgf. It's only finalized on paper at the end of the war.
Reference:
「
ジェットエンジンに取り憑かれた男」
by Takanori Maema, 2003.
「
橘花―日本初のジェットエンジンネ20の技術検証」
by Kazuhiko Ishizawa, 2006.
Was the Ne-330 an original engine, or was it a developed version of a previous engine?
Something interesting is that, though one would think of the more powerful engines as later developments, development of Ne-20, Ne-130, Ne-230, and Ne-330 were all more or less parallel, by independent companies.
1st trial production dates:
Ne-20: March 1945
Ne-130: May 1945
Ne-230: March 1945
Ne-330: April 1945
Ne-330 is Mitsubishi's independent project, not an improved development of the others, though the most powerful in plan.