A/C question

[f.monroe]

I converted the A/C system to 134a and I have a couple of questions. How many ounces are required for a complete charge on a 1977 Chevy truck ? What temperature are you guys getting at the center vent on Max ? I replaced the compressor, hoses , drier, orifice tube, and evaporator core . The only thing not replaced was the condensor and high side line . It gets to about 42 deg at night while driving . During the day it is just getting in the 60's at the center vent . I think it may be overcharged . Also , where can I get the black putty material that was packed around the lower inlet of the evap core . Mine was dry and unusable . The auto parts store said they didnt have anything like it and my case is open right now at that spot . I am sure I am losing a little air through the 2 inch hole and I need to seal it . Thanks in advance . Frank