i currently have a 306 block and my question is will my block need more work done to it to put a 331 kit or 347 kit in it? or can i just put it in?

 

331.... not really.......347 just a little clearancing.

 

so will it require more machining to put a 331 or 347 kit in?

 

no, you can use a die grinder and clearance the bottom of the piston skirts in the bore where the rod throw would interfere with skirts also you really need to have the pistons test fittted to the bore for out of round and or taper cause if you throw .030 347 pistons in a block already used/ bored .030 you may have inconsistencies that may or may not cause compression or blow by issues or wear problems...that's why when boring a block the machinist always wants your pistons before boring so the bore can be tailored to your pistons