i dont know where your pcm is but all you have to do is find the wire that goes to the pcm from the tdm. cut it and put the bypass circuit output to the side that goes toward the pcm. you can do that in the most convient spot you can find as long as the remaining wire to the pcm wasnt the problem in the first place. being older in this case doesnt change anything the signal was the same.
you still have to get the correct toothed key from the dealer .but once you have one, and the tdm bypassed you can go to the hardware store for cheap spares
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock