Tim,
you need to convert the variables you are retrieving into a string.
example: ToString(GetEventVariable({U 8}))
Your line should be something like this (check it first for the parenthesis):
0xfff0124e E 20 P "CreateEventWithVariables ( { C CURRENT_MODEL }, { H 0xfff0124a }, SetEventVariable ( GetEventVariableList(), { H 0x12b4c }, Append ( ToString(GetEventVariable({U 2})), Append ( { S \" - \" }, ToString(GetEventVariable ({U 1}))))))"
Cheers,
Daniel