Why use slip on flange?
This would normally mean having to go elbow-pipe-so flg.
I would suggest it is more appropriate top go with a weld neck flange, fitting to fitting with an elbow, reducer etc.
My 2c worth!
We are working on a project for a client and the client is supplying all material (which is sometimes a problem). All material has been purchased and received. Also, like you, I would prefer to use weld necks or even stub ends with back up flanges.
Thanks, Wayne