1995 GT dyno numbers

I found a site where a dyno shop post numbers for cars they run and lists the mods on the car so I looked for something close to what I have so I could entertain the possibilities. I found these numbers for a 1995 GT and they look really good but something just doesn't seem right. He went from 248 to 291.6 HP with no changes to the listed mods. The numbers basically show him hitting 290 to the wheels with only intake, exhaust, UDPs, TB, and MAF. Is this possible? If so, I should be able to hit 300 RWHP by just getting the same intake, TB, and MAF because he's still running stock heads and I've got GT40s, JBA shorties, Prochamber, and 5 degrees of global spark advance. Check out these numbers.

1995 ford mustang gt hp: 237.7@5110 tq: 287.6@3860
modifications: edelbrock performer intake,bbk shorty headers,bbk offroad x pipe,mac catback 2.5 inch,

1995 ford mustang gt hp: 243.3@5120 tq: 290.1@3970
modifications: edelbrock performer intake,bbk shorty headers,bbk offroad x pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 75mm maf,

1995 ford mustang gt hp: 243.0@5200 tq: 290.0@4000
modifications: edelbrock performer intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 75mm maf,

1995 ford mustang gt hp: 248.0@5300 tq: 289.3@3950
modifications: edelbrock performer intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 75mm maf,

1995 ford mustang gt hp: 291.6@5350 tq: 322.3@4080
modifications: edelbrock performer rpm intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 75mm maf,

1995 ford mustang gt hp: 298.4@5370 tq: 326.2@4050
modifications: edelbrock performer rpm intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 80mm maf,edelbrock performer heads,crane 2031 cam,fms 24# injectors,anderson motorsports cold air,

1995 ford mustang gt hp: 296.7@5600 tq: 320.2@4320
modifications: edelbrock performer rpm intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,fms 65mm throttle body,asp underdrive pulleys,pro-m 80mm maf,edelbrock performer heads,crane 2031 cam,fms 24# injectors,anderson motorsports cold air,

1995 ford mustang gt hp: 289.1@5540 tq: 318.7@4070
modifications: edelbrock performer rpm intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,anderson n/a power pipe,pro-m 80mm maf,edelbrock performer heads,crane 2031 cam,asp underdrive pulleys,fms 24# injectors,

1995 ford mustang gt hp: 289.3@5250 tq: 319.4@4210
modifications: edelbrock performer rpm intake,bbk shorty headers,bbk offroad x-pipe,mac catback 2.5 inch,anderson n/a power pipe,pro-m 80mm maf,edelbrock performer heads,crane 2031 cam,asp underdrive pulleys,fms 24# injectors,bbk 75mm tbody,