I'm sorry but I have to say I have never worked on a 3340, my sole experience of this model is a days silage mowing !!
However if experience of a 7245 is anything to go by, then remove the relevant head and see if there is any significant bore damage, hopefully there won't be since if it hasn't been used too much when poorly then there would have been no tension on the ring to cause damage, but you must be prepared for significant piston and bore damage.
liners are conventional wet , are usually not too hard to remove, and make sure the piston/liner kit includes the sealing rings that are around the liners in the block. Good luck !