If I may add my $.02 here.

I have, at last count, over 100 Futaba servos in current use. I have many 148's, 3003 and 3004. When the 3003/4 first came out I was disappointed that the 148 was being replaced. I bought a 3003 and took it apart to compare it to the 148. Somewhere in the archives I have that report but I don't know where. Anyway, from the fact that the 3003/4 is a little shorter in length than the 148 it is esentially the same servo. It appears to be designed for better automated manufacturing. The 3003/4 will fit where a 148 came out. Now what is the difference between the 3003 and the 3004. The 3004 already has one ball bearing installed on the top of the output shaft. I feel the extra $1 or $2 for the BB is well worth it. It cost more to retrofit the BB than it cost to go ahead and get it initially.

If you need a reversed servo, the 3003/4 can be reversed internally if you can handle desoldering. I have done that for an elevator servo.

Where have I used the servos? In addition to 40 and 60 size planes I have a Ultra Stick 120 with a Saito 150 that is using 3004's for all services, including flaps and rudder. I just put the 10th flight on a GP 1/3 Pitts with an OS FF-320 (4 cylinder). It uses 3004's on all controls except throttle and rudder where I used a Hitec 81 on throttle and a Hitec 605 on the rudder. BTW, the Pitts weights 20.9 pounds.

In my opinion the Futaba 3004 is the best servo available for the money.