Style chooser

Sifu, I'm using toyota seg ae111 converted to Blacktop with 5speed manual without LSD. My gearbox gone last week, went foreman thr replaced with another one. The foreman told me it is BT's original 5speed without LSD gearbox but what i felt is got different in gear ratio compared to the old one. How to test whether it is original BT's gearbox??? Before this 120km/hr at 5th gear = 3800rpm.. now 120km/hr at 5th gear = 3500rpm. I doubt he putting silvertop's gearbox.... any different between...