Dido on what 45/70 fan said , the forarm from your 243 will fit both the 45-70 and Tracker 2 barrels , i have the 45 and it is my fav barrel , just sold my Tracker 1 barrel in 12 ga. to get me a t2 in 20 ga.
As far as getting both at one time , i'd say yes it will save you some shipping cost and also some time without the frame as you will only need to send it in 1 time as opposed to 2 trips to the factory .
stimpy