The composition of a FedCom artillery battalion in 3050 is going to largely depend upon which part of the FedCom the parent unit is from along with the type of RCT it is attached too.
Lyran RCTs attach their artillery battalions directly to one of their armor units in the Armor Brigade and, as such, are largely self-propelled units.
Davion RCTs, on the other hand, attach their artillery battalions to the Armor Brigade itself instead of any particular regiment and can be either self-propelled or towed.
Normally, I would expect a mixture of Thumper and Sniper artillery pieces that basically mirrors the weight classification of the parent RCT, but I don't have any solid data to confirm this aspect.
Assault RCTs would have a higher mix of Long Tom artillery, although Sniper artillery pieces would still make up the majority of the unit.
Very few FedCom RCTs during this time period had entire Artillery Regiments, but there are a few in existence, so keep that in mind as well. Personally, I would expect this to the the only place you'd find an entire Battalion of Long Toms, and then only if the other Battalions were Snipers exclusively.
All that being said though, I'd argue that it doesn't matter what is "historical" so just build out your Artillery Battalion how you see fit. When I built the 33rd Avalon Hussars RCT, I gave it a full Battalion of Long Toms because of the fact that it was attached to an RCT built around a Reinforced Assault Regiment designed to be the heaviest unit in the Avalon Hussars Brigade, on par with the 8th Crucis Lancers and Davion Assault Guards.
Long story short, it's your decision.