I'm hoping the 767 FMC is the same as the 757!! If the Alt Cap happens shortly after T/O (before Clb is selected) the mode will be EPR/Alt Cap, as 757JJ says. in this mode the A/T mode is EPR controlled at the derated T/O figure (1.4 - 1.5 ish) and the ac will accelerate level like a scalded cat.
1. Select CLB thrust
2. Set VRef 80 in MCP window
3. Press SPD button on MCP
This will allow the ac to go to VRef 80 and no further while you clean up on schedule.
If you've already selected Clb it will open as SPD/Alt Cap (live speed mode) and you can wind the spd up to Ref 80.
If it's in G/A, that will produce Spd/Alt Cap - again a live spd mode.
Hope this helps
DH