Not too hard ,make sure you use good tools so you don't chew out the jets and round off bolts,if you are unsure about assembly only do one carb @ a time ,don't take too long to do it otherwise you tend to forget where things go
,take lots of pics also.
Order genuine Weber kits as they have parts that fit properly,some aftermarket ones leave a bit to be desired,order the kits ahead of time, clean them really well before assembly.
Lots of info online to set them up so no issue there,do all your primary settings before you refit them as saves constantly removing them to solve issues ,you will need to do the following;
check float levels,
set throttle stops,
check enrichment lever adjustment,put fuel in the bowls ,check for leaks and test accelerator jets for clean even spray down the throats,
set mixture screws to 2.5 turns out .
Good luck
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