Gary Puckett & the Union Gap cranked out five studio albums between 1967-9, with a greatest hits album released in 1970. Signed to Columbia, the band produced the albums between February 1967 and December 1969. In the summer of '68, the band appeared on The Ed Sullivan Show to perform "Lady Willpower", which peaked at #2 on the Hot 100, but hit #1 on Cashbox's chart. Cashbox was a defunct music magazine and rival to the still-running Billboard.
I think Puckett was an influence on future Doobie Brothers vocalist Michael McDonald, just in the style of his vocals.