Whatever plane you use still has to deal with the problem of the B-29's size and defensive firepower. It can survive a lot more punishment than any fighter ever will and the remote controlled turrets can do quite a number on the attacker before they'll to take it down. I'm not saying that the bomber could fend off every attack, but it could definitely survive quite a few because of this. If, on the other hand, the interceptor were armed with unguided air to air rockets, the bomber's size would become a weakness since it presents such a big, slow turning target for a one-hit-kill weapon. IOTL, the Germans used one of these weapons with their jet but theoretically, I think it could have been used with any platform that could carry it.