46 i assume springer. Inline i assume one of the different springer setup with different trail?
Yes if this is reducing the frt wheel trail, it will help reducing the force needed to turn the handlebars on your sidecar rig. There are several important things that need to be correct if you shall have a reasonable and safe rig. In my view the side car toe in is more important than the frt wheel trail. You need to get this correct first. Side car wheel lean and trail compared with bikes rear wheel also play a role. Frt wheel Trail should be less than a solo rig. Very important to have a friction bolt through the steering neck when trail is reduced. Old sidecar outfit like the BMW R50/2 had one. A steerin damper will do the job. A sturdy fork is a must. Springer look cool and i love it on my solo bike. But it should never be fittet on on a sidecar rig. For a sunday trip all right. But thats your choice. But dont expect much if you stay with the springer. Earles fork like the said Beemer is the best. Hydra got one with an adjustabel steering head for sidecar use if you need to stay with factory parts.
How to install, adjust and test? Try this page. http://www.sidecar.com