4020 pistons gets you 4.25 bore... Can go to 4.625 and still be very reliable. there's a 4.5 inch piston thats fits real well also. Out of an International gas V8, don't remember exact application at this time. Have to check my notes... 5" can be done if you want to spend the money.
What kind of class/rules you looking to fit?
Will take a well built A to keep up with a mild 44. 44 is comparable to a G in size from factory HP... Just wieghs 1000-1500lbs less... 9 bolt wheels without special hubs or adapters. Easy to balance. Tough rearend will take abuse.