Im alittle worried here. You are planning on swapping in a LS2/6speed into a V6 auto car...cutting this hole for the shifter (i assume) is the least of your worries...
Non the less... the easiest way to do it, is to wait until the trans is installed. Take the shifter off, cover the opening really good with rags and some tape. Once the trans is in place, use a punch and from under the car, make a punch mark at the 4 corners of the shifter location. Then from up top, cut about 3/4" around those punch marks. It doesnt have to be exact...the rubber boot that bolts to the floor will cover it. If you are unsure, lay the boot in place and make sure it will cover your hole.
This is the easiest way to make sure you get it right the first time and dont hack up your floor. If someone has a nice picture of the tunnel, with dimensions from certain points that will allow you to be accurate, then thats a way to go too...but if you wait til the trans is in...you will see exactly where it needs to be.
Good luck!
Justin
P.S... And which car is this going in? You mention an 01, but I see 02 Z28, and a 91 RS in your sig. You have an 01 v6 that you wanna convert too? Just curious...
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ARE shortblock, Ross custom boost pistons, arp rod bolts, ARE ported oil pump, MTI 2e 5.3L ported heads milled .015 with double springs, 228/224 113+1 Comp XE-R, Cloyes adjustable timing chain, LS6 valley cover, fast 90mm intake, NW 90mm throttle body, SVO 30lb injectors, 85mm MAF, ASP underdrive pulley, 160* t-stat, stainless LT headers 1.75" primaries
Correct dimension auto to M6 
