[cctalk] Installing DEC C on RSTS/E

Hi... I'm seriously rusty on official RSTS installation procedures. I'm trying to install DEC C using the C_V1_2.tap file from the bitsavers bits/DEC/pdp11/rsts directory. It's actually a TPC file, in spite of what the extension suggests. Once I supply the correct format, SIMH recognizes it and RSTS can see the tape contents. Then I try @[0,1]install c81. Point to the tape, answer the destination, and then it asks me for the "library" tape and complains when I give it the C tape again (labels don't match). So what is it looking for? Does anyone have the C installation procedure handy? paul