I keep getting different answers to this question I have a 10 bolt and mono leave I would like to change it to a multi (4) besides the leaf what else do I need to change thank you

 

The lower shock plate under the springs.

 

If they haven't been already, replace the original stud bolts with u-bolts, they'll be too short anyway. With the studs, the spring attachment is only as strong as the spring perch to tube weld. U-bolts make for a nice strong sandwich.
And unless by some strange chance your rearend has them, you're going to need to drill a centering hole in the spring perches for the leaf spring pack bolt/upper locating pin. The mono leafs have a locating pin only on the bottom where it fits through the lower plate.
Also, if the gap between the lower plate and the spring perch is too great (because the springs are thicker) you can leave out one or both of the rubber insulators.

 

Thanks guys that would be my first winter project after Thanksgiving depends how the weather is am also putting a 10 bolt posi 373 gear next question which is easyer taking the old rearend and leafs all out at once or do leafs first then reared / houseing

 

First, get a couple flea market 9/16" bax end wrenches and heat the handle and bend to fit the J-nut inside the rail as the nut is merely crimped in place on the clip. Some nuts just spin and the bolt head will need cutting off, then you have the nut/clip rolling around for life as there is no way to remove it.
OR, remove the back seat bottom and drill a 1" hole above the nut and use an extwension and deep socket to hold the nut while loosening.

Hopefully, the bottom shackle bolthead points to the qtr panel for easy removal of bolt to drop the back half of the spring, then the rear axle will simply rollout. Otherwise, the gas tank has to come out to remove the bolt to drop the spring.

Use antiseize on the bolts and nuts during assembly for future removal. You will be glad you did later in life.

If one person is swapping out, do the springs and rear axle separately.
Disconnect axle, disconnect springs, roll out axle, drop springs.
Assemble in reverse and use grease on the front bushing and through bolt in spring eye.