Not sure what this did to the floorpan of the Avanti body - maybe it tucked inside the rockers? Dunno.
The G frame was actually pretty good, and it came with the 305 / TH powertrain; having a flashback it may have been the L69 HO engine?
Former Pontiac SD and high-performance guru Herb Adams helped the Avanti folks prepare a 'new' model for SCCA showroom stock competition in the mid-80s, and all was going swimmingly until the G-Body went out of production and Steven Blake (who had moved production to an abandoned bit of mill space in Youngstown, OH) got in the marbles financially.