Your 5 speed cross member will work with a 98-02 F-body T56. Your driveshaft is too long as well as you need the smaller TH350/4l60e yoke.
They say a 4l60e reluctor wheel for the speed sensor will fix the loss of cruise control issue on the M5 to T56 swap.
Truck master cyl and braided line will hook up to the T56 slave cyl.
Reverse light plug works as well as speed sensor.

It's really a very easy swap.

Lord Aries (I think) did a write up on a 3/4 ton 6 speed into an Avalanche. Some of his info may help. You shouldn't have to cut a new shifter hole with it.

Or you could just get a Gearvendors unit.
http://www.gearvendors.com/

 

Gibbs, the GV are sweet but pricey.

Cause I looked at em. Bulletproof tho, Heck, they're stronger than most any built trans. - the TQ. capacity is insane.