This is only slightly O/T...
It's the lineup (allegedly) on the original version of "Moon Dawg". I found it five years ago at an unnamed site:
MOON DAWG! - The Gamblers [2:15] (Derry Weaver)
DERRY WEAVER: lead guitar
ELLIOT INGBER [later of The Mothers/Magic Band]: rhythm guitar
BRUCE JOHNSTON [later of...]: piano
LARRY TAYLOR [later of Canned Heat]: bass
ROD SCHAFFER: drums
NIK VENET: dog howls
Produced by NIK VENET
World Pacific single #815 (1960).
Another source credits Sandy Nelson as drummer on #815; and that Leon Russell played piano----as well as Bruce, apparently----which is possible judging from the full, almost Spectorian sound.
Yeah, it's one of those records that everyone claims to have been involved in in one way or another -- so there were claims that Russell played on it, that Kim Fowley is on there, that Sandy Nelson was on there, that the piano player was actually Howard Hirsch (who played on the Gamblers' later singles), that Derry Weaver was a pseudonym for various other famous guitarists... it's one of the ones where if you believe everything that was claimed about it, half of LA was in the studio.
But I looked into it a few years ago, and came to the conclusion (though I couldn't now tell you *why*) that the lineup you list is the correct one. Certainly Bruce is in the harmonies on that track, and it sounds to me like his playing, too.