e1994c, a person wonders why you are not just buying a standard fitting, but...
If designed to Sec VIII, Div 1 you will have to follow the rules of UG-36(e) and Appendix 1-5 for internal pressure and, if applicable, UG-36(f) / UG-33(f) and Appendix 1-8 for external pressure.
If your cone-cylinder junctions are considered as "lines of support" there will be restrictions on the minimum cylinder lengths, if not, there are none.
The forgoing applies to 2017 Ed, 2019 Ed may have different requirements.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
Note: Edits in bold