[Unclenick]

The forearm usually comes from sustaining a hard grip for too long. It leads to what is commonly called "shooter's elbow"; basically the same thing as tennis elbow. You can look up all the standard PT (physical therapy, in this case) exercises for tennis elbow and do them preemptively.

It may be the shape of the Taurus is exaggerating that for you? Swapping the mainspring housing is undone by putting the original back, so you could try that to see if it helps. Just keep the original, and you won't affect the gun's value.

For awhile, a lot of Bullseye shooters got left hand twist barrels which were supposed to ease the elbow problem. For me, it exaggerated the problem. Bullseye shooters are shooting offhand (one-hand hold) so this gets to them more frequently, despite the loads usually being lighter. People using two-handed grips are prone to the weak hand pulling the wrist of the strong hand, such that the two fight each other. Sore forearms and shooter's elbow also result. You can try retraining your grip by going through the motions at a snail's pace to identify and consciously neutralize the undesirable force if that is the problem you are having?