What's that 4-pickup NR in Craig Gruber's hands?
Something he obviously played at the sessions for Rainbow's debut, but I don't know if it was also on the recorded versions - could very well be by the sound of them.
He also played that bass live with Elf when they were still regularly opening for DP. There is a pic of him in the inner gatefold sleeve of Rainbow's debut, but that is from Elf days, Gruber got fired (like all Elf guys with the exception of Ronnie Dio) before he ever got a chance to perform live with Rainbow, they just recorded the debut.
You can see him play it here (audio unfortunately heavily distorted, but a historic artifact, no other footage from late period Elf survives, they were a great band).
On Elf's last album (recorded around the time of the Rainbow debut and hardly released at all so as to not conflict with it) the bass could well be that TBird:
https://youtu.be/U7Ms3vS-yDk?si=ROA0wT9xOQJWOY7FSame on the Rainbow debut, with this track being particularly Elf'ish: