New wheels/Tires before New engine installation?

Greetings!

Regarding leveling the engine during installation, I’m just wondering what the general thinking is about having your ride stance set before installing a new engine.

The car (69 Barr) currently has an old set of roller wheels (original 14”) and Tires (26” tall all the way around).

The wheel/tire combo I’m thinking about will be about 1” (255/60r15 - 27”) taller in back and 1” (215/60r15 - 25.2”) shorter in front.

Should I finish and install the engine, or purchase the wheel/Tires first? Or, doesn’t it matter all that much for my setup?