Weldolets® (aka integrally reinforced forged branch outlet fittings, or integrally reinforced branch connections, IRBC) are only compliant to MSS SP-97 when the schedules on both sides are the same, and only in the schedules STD, XS, XXS, and 160. Also, they are only true Weldolets® if manufactured by Bonney Forge (although everyone uses it as a generic term). But basically, if you aren't using one of the standard schedule combinations, you are required to follow the requirements of the particular piping code you are using for design of branch connections (and some piping codes still require doing reinforcement calculations even with fully compliant SP-97 fittings).
Theoretically, use of any type of IRBC with main and branch schedules not exactly as per that MSS document is outside of the scope of SP-97. However, my company allows the use of any heavier scheduled IRBCs than the actual piping, as any reinforcement requirements should be more than met. So in your case, if I was specifying a standard IRBC, I would be looking for a 24" S160 x 8" S160 fitting (assuming you are using true schedule 80, and not XS). But a STD x Sch 80 will definitely not pass in your case, regardless of compliance to MSS SP-97 or not. If you really needed to try and make this fitting work, you would need to have all of the exact dimensions from the manufacturer, then do branch connection reinforcement calculations to whatever piping code you are following. But most manufacturers are not willing to share those dimensions, they consider them to be proprietary, and would only share the dimensions that are publicly available through MSS SP-97/
