Lead shot in the frame is a very bad idea as far as handling. The weight will transfer way to much under acceleration, braking & cornering. I’d bet that anyone who has tried this has realized it’s a bad idea. The only way you could POSSIBLY get it to work, would be to use a two part foam to plug the frame both before and after inserting the shot, effectively packing the weight in, and not allowing it to move at all. But it’s going to be a hell of a time removing it. Lastly, I’ve always felt its best to mount weight somewhere within the envelope of between the front and rear wheels. The torque that the weight would have could also really cause serious handling problems IMHO.