I have never seen 7 x 1.25 used on any Toyota, its most likely 6 x 1.0. take it to a fastener shop and they will measure it for you. Pictured is a pitch gauge it will tell you the pitch.
Toyota mostly used ISO metric the number in the center of the head is the tensile grade.
6 x 1.0 = 10 mm head across Flats
8 X 1.25 = 12mm head across Flats
Its basically the same bottom end just get it to breath better,bigger valves, porting, free flowing exhaust, face the head. and you will have better performance.
If the ACT RTA is anything like The Transport SA you had better book your taxi now for work, your about to experience getting stuffed around by professionals.
Ball Bearing balls are great to block off vacuum hoses, get a size that fits the hose tight.
refit the hoses in the correct positions and it will all still look compliant.
Once you have finished drilling, tapping ect you should try polishing aluminum with steel wool and Velvet soap, Don't use any nasty waxes ect it may interfere with the welding.
I think You made the right decision to keep with the 7k flywheel as they are factory balanced and the engine will run way smoother with the correctly balanced flywheel. with the custom clutch setup it should be bullet proof.
I think the car is looking good.