Thats definitely horseshit.
I've been a 3rd gen F-Body enthusiast my whole life, I've researched, own or have looked up all possible documentation on this, and this is also very old news to those who frequent
www.thirdgen.org.
GM definitely DID make L98/T5 cars, however NOT FOR SALE FOR THE GENERAL PUBLIC. All the test or "mule" cars they made no longer exist and were all destroyed. GM found that the T5 could not handle the sheer mass amounts of torque that the L98 350 produced, so instead it was only officially paired/offered behind shitty 305's.
Even a G92 1LE was an LB9 5.0 H.O. making 230hp and 300ft-lbs at its best, matched with factory 3.73 gears, those rare G92 5-speed manual cars were a treat to drive, handled great etc but straight line performance was less then desirable (mid to low 14's stock).