wood to pellet vent help please

[phxwolf]

we run a small dog rescue/sanctuary, and to heat kennel we had a wood stove that we had to replace,
i found a real nice gently used Englander 25-pdv. the old stove had 6" pipe. the 25-pdv has 3".
the new stove is also offset from hole in ceiling due to old unit pipe was straight outa the top, and 25pdv is out the back and off to side.
what parts would i need to either run 3" all the up the 6" to the cap, or is it better to find adapter to connect ceiling box to 3" vent from 25pdv"?
........if i do run 3" inside the existing 6" would i need to seal gap between 6" and 3" pipes? thank you.....pics attached

 

[Ssyko]

I would use an adaptor to go from the existing pipe to the stove 3"

 

[phxwolf]

Is there a model or part number for that? Would duravemt have it?

 

[Ssyko]

This is what i used and sealed it with high temp silicone

(broken link removed)