51GMC P/U with an 86 Camaro front clip. Truck drifts all over the road.

IF there is still excessive lash in the gearbox , after adjustment , then maybe it's defective? What else in the front end has been inspected for wear? Explain , maybe a little differently , what you mean by 'drift'? What kind of symptoms?

Your front clip is most likely attached to the trucks frame at a lower angle than the stock 86 Camero factory angle.You may have changed the castor settings by changing the height at the rear of the clip frame.Have the front suspension re-aligned to the factory Camero settings and your truck should drive down the road just fine. Lowering the rear of the frame or any vehicle removes castor,raising it adds castor and adding makes it track straighter.Don't overlook rear sloppy suspension components which can also make for a tiring driving experience when one has to keep correcting to stay in your lane.Dave