mech Roller vs Mech flat tappet cam Q

Question one; You are correct.

Question two; This is something you worry not.

The larger .904 lifter has the advantage to handle a steeper ramp, quicker rise rate cam. AKA, bigger more aggressive cam. Load handling ability is a combination of parts and material used. AKA, proper valve springs and acco. parts on the head. Pushrod strength, good metal in the making of the parts and of course, lubrication.

While I'm sure a larger diameter tappet can handle more load, I have not noticed the smaller diameter tappet engines having any problems. Of course, when they get super serious, there tappet diameters go to 1 inch.