When the time comes to install and fill the transmission, make sure you only use GL4-rated gear oil. Do not use GL5; it is not backward compatible for all transmissions. As a part of its rating GL5 must withstand extreme pressures, which sounds great. To achieve that rating, though, the gear oil must contain sulfur. Sulfur dissolves yellow metals--including those brass synchronizer rings you just bought.
99% of gear oils on the shelf locally will be GL5-rated. The only two GL4 oils of which I'm aware are Red Line MT-90 and Penngrade 77296 but there may be others. I use the Penngrade because the pretty green color reminds me how expensive this hobby is without looking at my bank account.
Other than Red Line, none of the "gee-whiz" high-dollar synthetics (SynPower, Mobil 1, Royal Purple, etc.) is compatible with brass syncrho rings--no matter what the company rep tells you.