/6 exhaust washers

Super dumb question here:

My 273 w/factory mani's had some of those cone shaped washers, dunno how many before the manifolds came off...I'm going back with the Dakota logs on and have shaved .250 off of flange surfaces. I realize bolt/stud lengths will be different but how important are those washers to go back on and were they on all bolts/studs? Is there a substitute for the washer?

What do I need?

Thanks FABO!

Thanks