line up bar is a dead straight section of bar which will sit in machined pucks which simulate the carrier and axle bearings giving you a case which is true. You can buy them from Mark Williams, or use a length of TGP steel bar, or an old long hydraulic ram is a good alternative.whats a line up bat?
I presume a length of bar/ tube all the way throught the axle while re re'joining
Its just a toy / street car maybe a daily ? No big power no straight line action.What are you building a street car or a race car.
I narrow a fair few axles. On street stuff i just keep the c clips. If there good enough under millions of yanky cars,there good enough for general street use on a rod