Loading 357 cases with Win 231

I am currently shooting reloaded 38 caliber cases in my S&W 586. I'm using a 148g HBWC over 3.5g of Winchester 231. I am looking to use 357 cases and my question is what is a good starting point for the powder that I have if I use regular small pistol primers instead of Magnum primers? Thanks in advance.

Are you using hollow base or bevel base bullets?

I would probably start with the Winchester 38 SPL load info based on bullet base type
and not make any change based on magnum primers.

Winchester's 15th Edition Reloader’s Manual showed this for 357 MAG:
148 grains WC WIN 231 3.4 grains 880fps 19,500 cup
(NO INDICATION OF HOLLOW OR BEVELED BASE)

My Speer number 11 manual shows this for 357 magnum:
148 gr HBWC Win 231 3.4 grains 747 fps 
MAX load 3.8 grains 811 fps
(higher than 3.8 grains not recommended with Hollow bae bullets)

The Winchester info for 38 SPL showed a tenth of grain less for the hollow base bullet with Win 231.
148 gr. Lead 2.9gr 231 690fps 12,400 cup
Hollow Base WC 3.3gr 231 770fps 16,100 cup

148 gr. Lead 3.0gr WIN 231 690FPS 13,600 CUP
Bevel Base WC 3.4gr WIN 231 760FPS 16,400CUP

From this

An additional source of load data is Hornady's Reloading Data Center.  Their load for 231 in 357 cases (148 Hornady LHBWC bullet) is between a low of 3.0 grains, and a high of 3.4 

Link to site:  https://www.hodgdonreloading.com/reloading-data-center?rdc=true&type=53

NOTE:  Hodgdon is the distributor for Winchester powders.

Hope this helps.