Scott:A 12 volt pack might be a bit much, as the AA batteries for the R/C T-34/85 are Ni-Cd rechargables, and really only supply 9.6 volts at peak. You might damage the circuitry by putting 12 volts into it.
As for amperage, thats not an issue, as the components only draw as much amperage as they need. In fact, guys run higher-amperage packs to gain longer run times.
You wish to know more about modifying the T34/85, you could join Yahoo's
MaruiTankGroup or
BigBandaiTanks , both which deal with T-34/85 modification.
Hope that helps you out,
WhiteWolf McBride
Ontario, Canada