Unless you are changing brake calipers, your best bet is to keep the stock bore size. Bigger is not better. Brake masters are sized according to the cross sectional area of the pistons in the brake calipers and the rear wheel cylinders. Other things come into play such as pedal ratio and brake booster area. $200 is a very fair price for a brake master that you know will work properly and won't require all kinds of other potentially costly mods to make fit. If you are determined to try and use a $50 Chinese master, then take careful measurements of the stock TR7 master and use that as a guide to pick out the new one. Sites like Summit will provide measured drawings of the parts they sell and in some cases application. The biggest issue you will have to overcome is the small size of the opening in the booster that the master inserts into. Most aftermarket MC bores are between 7/8" and 1 1/8'. The castings are too large to fit into the TR7 booster. Bigger MCs are great if you go to larger caliper bores or add rear disc brakes. In those cases, you will want to push more fluid with a given stroke of the brake pedal. You will also need to buy a handful of brake line adapter fittings, and plan on modifying the brake pedal and the push rod. Buy the new one, a good used one, or rebuild the one you have.