Drivers who won features in both a modified and sprint, both built by same builder:

Dick and Scott Tobias- Tobias chassis. Ironically Dick won modified features in cars built by others, and Scott did the same in sprints.

Kenny Weld, both built by himself.

Jimmy Horton- Tobias chassis.

Stan Ploski- Buckley chassis, 

Bobby Weaver-Weaver chassis. Bobby also once won the modified and sprint features at Port Royal on the same night.

Gary Gollub- Tobias chassis. I’m told that Gary also won a modified feature in a Weaver chassis for Bill Brian but don’t think he won in a Weaver sprint.

Bruce Thompson - Buckley chassis.

A few “close but no cigar”. Drove both by same builder but didn’t win in both. Lee Osborne, Kramer Williamson, Kevin Collins, Freddy Sabatino. 

A couple “gray area” honorable mention: Gerald Chamberlain won features in both modified and supermodified built by Gus Frear, and Doug Wolfgang won in both built by himself (the sprint is called a Trostle but Doug designed and built it, and a South Dakota modified doesn’t really resemble an East Coast modified. 

There were more (and more possibilities)than I initially thought, thanks for replies, and feel free to add on.

Rick-  Your post is just another example of "I learn something new every day!".   In particular, a modified here (NJ, Pa NY) is not necessarily a modified in other parts of the US.  Scott Ely

Rick, do you know what type of Chassis Toby Tobias Jr. ran when he raced Silver Crown Cars?

I believe Richie ran a chassis of his own design.

I’m pretty sure Richie built it himself.

Won most, if not all, his sprint features in cars he built himself, but best he did in his self built modified was a second.

I can't remember but Richie either turned his sprint car into a champ dirt car, or his champ car into a sprint car.

I don’t recall Rich ever driving a sprint. He did start his career in a super sportsman.

Richie did win the Silver Crown race on the DuQuoin mile in 2003, per the ‘Toby’ book.

TOBIAS CHARGES FROM 25TH TO 1ST TO WIN AT Du QUOIN Du Quoin, Illinois………Rich Tobias Jr. of Annville, Pa. finally shed his bridesmaid tag in the USAC Weld Racing Silver Crown Series on Saturday night, winning the Ted Horn 100 at the Du Quoin (Ill.) State Fairgrounds. The race, rained out a week earlier, was held under the lights for the first time in its 55-year history.

From USAC - Silver Crown Results

Just heard from Kevin Collins crewman Hunter Frey. Kevin did drive both a Tobias sprint and modified. His sprint was the former Statewide 3 of Jimmy Horton. Kevin won the URC feature at Jennerstown the night of the crash that ended Jan Opperman’s career. The modified was his Falcon, no wins in that car.