The LT-40 would ba an ideal trainer for that 46AX, the best trainer I've flown. The only way I can see that the LT-25 would be better is that it would give you some tail dragger experience to prepare you for the J3....

If you haven't already got the LT-25, then the best option I think would be to get the LT-40 or similar. It could be converted to a tail dragger later. If you have got the LT-25 then you have a mismatched pane and engine and may need to get a smaller engine. On the bright side, a decent 46 2 stroke is always handy to have laying around...