I have an MC21 that has been stripped down to crank over winter and rebuilt with adding HRC stuffers and rear head conversion, i also plan on drilling airbox but think its best holding off doing this major change (that will upset jetting massively) until the motor is bedded in.
Bike was on standard jetting with no mods except dogfight pipes. Engine had new crank bearings, pistons and rings.
I have no experience really with 2 stroke jetting other than cleaning and rebuild carbs so my questions are.

Do you think i should just drill airbox and then start off with bigger jets (around 150's) and then work my way down as normal or dont mod airbox yet and just go 1 or maybe 2 sizes up to allow for the slight mods (stuffers and head conv)to allow me to get engine bedded in without added trouble of possibly fowling plugs then when all is well drill airbox and jett to suit?

Also any recommendations on starting points for jetting or which size jets to buy as i dont have any?

Advise greatly appreciated,

Andy