quit trying to do something there's no need for? while it is possible to do it, there really is no reason to downshift to 1st, you should be going slow enough for brakes to finish the job, yet still accelerate away in 2nd with a 283 if you don't need to come to a full stop .... you could also look for a 68+ 3 speed, they have a syncro 1st and pretty much bolt right in
Bill