Two things to watch out for:
1) Early and late TR6 calipers were different, and took different pipes and mounting bolts. The holes in the caliper became a metric size, while the threads in the mounting plate remained SAE. Ditto the brake line threads. IIRC the Toyota parts are metric, so you'll need to source the special "adapter" pipes and bolts for your early TR6.
2) It's very important that the brakes match exactly from side to side (otherwise the car will pull badly when brakes are applied, a dangerous situation). So you can't convert just one side.
The stock front brakes are plenty adequate to lock the tires, unless something is wrong with them. Plus, with no proportioning valve or ABS, front/rear balance is very important on these cars and will be upset by any change in "stopping power". In other words, "improving" the front brakes may actually INCREASE minimum stopping distance, unless the front/rear balance is adjusted to match (typically by using rear cylinders with a larger bore).