where to put draft regulator when using 8" to 6" reducer

[tallywhacker]

I currently have 6" furnace outlet that goes to a masonary chimney that's 7" by 11" and around 35'-40' tall. im using a manual damper in the flue, that I have close to about a 45 degree angle to keep from over firing the furnace when the inlet air is set to high position. which tells me I have a very good draft. im looking at a new furnace that has an 8" outlet to chimney. iwas thinking I could use a reducer to go into the chimney, and put draft regulator in the set up. new furnace calls for .06 draft. also thinking of enlarging the opening to the chimney to 8". not sure what to do, any ideas from you guys?

 

[brenndatomu]

also thinking of enlarging the opening to the chimney to 8"

This ^^^