About the differences from Japanese N-I page 
 Partial information of this article is different from Japanese N-I page.  The citations may indicate that N-I and N-II are derivative of Delta, but not itself.  Especially, the 2nd stage of N-I is different from Delta (under-mentioned).  There might be estimation on the analogy to N-II, which employed all Delta stage. 

 I think that the JAXA official N-I web page is more appropriate for the citation of dimensions.  The same data are seen in WHITE PAPER ON SCIENCE AND TECHNOLOGY 1982(in Japanese, see table 1-2-24). 

 Besides, according to the white paper, the propulsion system of N-I's 2nd stage was developed by domestic technique, and thrust and specific impulse of the engine, called LE-3, are 5.44 ton and about 290 sec, in vacuum, respectively.  The LE-3 is seen in the JAXA Photo Archives.   

 By the way, it seems that N-I have 3 (not 9) boosters in the many pictures of N-I in the citations.  According to the JAXA Photo Archive, N-I's thrust is about 150 ton (1st stage 80 ton + boosters 70 ton).  It seems that Thor-ELT + 3x Castor2 is more suitable for the thrust.