PCM programming is also different in the 9C1. Fans turn on sooner and stay on longer, timing is more aggressive, no speed limiter, etc.
As far as doing the top swap goes...I'd imagine it can be done, and it has been done. As stated, he already has the hd trans, AND the lower gearing to boot. Top swap it, along with the accessory drive from an L67, the harness, and reprogram the PCM so it can include the boost control. But, don't keep the stock boost. Lower it to about 6-8 psi, and have it come on later than normal, as your numerically higher gear ratio will more than make up for that (assuming you kept stock L67 tables, you may have a hard time keeping traction).
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.