A;
...there's nothing wrong with improvising, as long as your improvisation applies the (significant) forces in the same manner as the approved pullers: That is, pushing concentrically on the shaft (nut replaced loosely after turning around) in order to apply pulling force on three (or more) studs.
Applying forces
any other way will not work, or bend or break drum, or bend studs or some unsatisfactory/disastrous combination. DON'T DO IT!
People have made their own (blue one shown in link is a (good/approved) home made version) OR you might find one at a service place that works on vintage trucks.
Good Hunting!
Ref:
http://www.sw-em.com/Brake_Drum_Notes.htm
Cheers from Connecticut!