I've just built a house myself. Doing this is easy I am copying what was fitted and the position of the brackets. The reason your saying people have a hard time lining it up must be the chassis is made slightly out of position. A jig is only for speed so you dont have to measure. I am measuring the chassis just now and bulkhead mount on one side had been replaced and its 20mm out compared to the untouched original untouched side. These chassis manufacturers are making as many as they can as fast as they can. Different guys are making them human error. Rc chassis started in a chicken shed . Both chassis legs are identical. A jig just let's you bang on the brackets without measuring or checking it not some hydraulic pulling machine . We will see it's just funds that will slow me done as I said we have spent alot on 1 2storie extension side and 1 kitchen extension