By 1990, the 426 Hemi type motors were the only motor being used in the nitro classes for reasons given above (ease of maintainence and performance using a blower and nitro).
The 426 Hemi rule came not long after Bernstein invested in and was testing the McGee 4valve OHC motor. The Hemi only rule was to slow the rising costs of running in the nitro classes.

Best I recall, the last TF car that won a National event (Springs I think) that wasn't 392 or 426 based, was Jim Bucher's Chevy. He was an underdog favorite, ran 3 or 4 years in the early '70s on a small budget, a Chevy motor and still managed to win some rounds.