to change the t-stat on any 3400 engine removing the throttle body is an unnecessary step. the bottom or rearmost bolt holding the t-stat housing in place is slotted and doesn't need to be removed fully there is enough room to get it all out without removing the t-body or cross over pipe. i've done it a hundred times. the write up was well done i'll give it that but making more work than needed. sorry.

 

Have to do the work too on mine and found this link that shows it properly:

YouTube - GM 3100,3400 Thermostat Replacement

 

i wanna know if you need to bleed the after changing the thermostat

 

Yes, as you'll have the cooling system apart so you're going to loose coolant and air is going to get in the system. Make sure you add the neccesary coolant and bleed all the air out.