Nelonga‘s suit was the one remodeled from Pagos of Ultra Q.
Initially Pagos’ suit was remodeled from Baragon which was a Toho monster lent out to the Tsuburaya Productions.
The head of Baragon was replaced by that of Pagos for Ultra Q, and then Nelonga for Ultraman.
Therefore the body of all these monsters remained the same as Baragon with the characteristic fins on the back though the black spines covering Magulla’s back made the fins invisible.
It was described in the past that the head of Nelonga was sculpted by Akira Sasaki known as the sculptor for the masks of Ultraman and Ultra Seven.
But he himself admits he doesn’t remember it, so it was possibly sculpted by someone else.
All these monsters above were played by Haruo Nakajima, the original Godzilla actor, who states the monster suits for TV products were too light for him.
Baragon was made by the Toho SFX Art crew to make it fit Nakajima, and I guess that’s why he played all the monsters above.
Tetsuo Yamamura says the inside of the suit had urethane just exposed unlike Takayama-made suits covered with cloth inside and that the suit was so heavy in weight.