I am interested in how you think these hands should be bid using 2/1 GF methods (playing matchpoints if that matters).

In our methods, opener's 2♠ rebid shows 4(+) ♠s but does not promise any extra values.

IMO, responder's 3♣ rebid is not necessarily natural (could be looking for ♣ help for 3NT), but that perhaps is just my opinion as I"m not sure partner and I have a clear agreement.  So I would be interested in your opinions on this point also.  IMO, the 3♣ rebid would be consistent with something like Axx-xx-AKJxx-Jxx.  My view is that responder would normally rebid NT with ♣s unless his hand were strong enough that he planned to continue with a 4♣ third bid (e.g. over opener's 3NT) to show slam interest.  Your views?

I believe these hands should be bid to 6♣ which makes on actual deal, and a simulation showed that these two hands will make 6♣ on about 70% of random deals (double dummy play/defense).  

In our club game, NO PAIR reached 6♣.  One was in 6NT and one in 6♦, both -2.  Everyone else played 3NT with four pairs (including us) making 4 (always possible double dummy) and the other two pairs making only 9 tricks in NT.