The Gunning Brother's 57 4 door wagon, The Jolly Green Giant, ran a similar combo during the 67/68 season and it actually ran H Stock. I don't know, but I'd guess it was the 283 CI small block. Somewhere there were class index posted for the stock class'. You need the advertised curb weight divided by the C.I displacement to find the class. in 1968 the G/S class is 11.00 to 11.49 , H/S 11.50 to 11.99 so on up to U/S which is 27.0 and up. Anything under 8.0 lands you in Super Stock. A/.Stock is 8.0 to 8.49. Somewhere in the 80's NHRA ruled out the Tri 5 cars, I don't know what the rules are today, but it's effectively limited to late model cars. Just one of many NHRA missteps in my opinion.