Actually, you DON'T want the engine at TDC when you set in your distributor.
Put it where you want your initial timing to be, for example if you want your timing to be @ 10 deg, put the engine at 10 deg BTDC, drop the dist in, rotate it so the the firing mechanism is lined up on #1, and you are good to go. No timing light needed.
Remember the dist has 360 degrees while the crank has 720. If you aren't pointing at #1 that means #1 is at the end of the exhaust stroke, so really #6 (Chevy, Mopar) or #3 (Ford) is the one actually ready to fire at TDC.