1st gen Tundra - what size tires will fit without lift?

I've got a 2006 Tundra 4x4. Stock tires are 245/70/16 = 29.5" x 9.6" / 16". Can I install these tires without doing a lift? 265/75/16 = 31.6" x 10.4" / 16". This would be 2.1" taller and .8" wider.

Yes. My brother installed these exact tires on his 04' double cab on the stock wheels with no lift. He has run them for around 40K with no issues.

The 265/75/16 is a nice size for the Tundra. I had 285's, 2" lift and didn't handle as well on the road. Off road was a different story. If I did it again, I would skip the aftermarket UCA's, install the IVD coilovers again and keep it a bit lower. There seem to be a lot of 275/70/16 LC take offs around for sale. That might be a good size Michelin AT tire without lift.

someone suggested I needed to put 1.25" spacers on the front if I have these tires. Is that so?

No. The 265/75s will fit without anything else. Taller or wider (255/85 or 285/75) will require a lift, or pinchweld mods - or both.

I am running 265x75x16's on my 06 with no problems no lift etc.

I am always leary of spacers etc. because of the additional load placed on pieces and parts not designed for the extra load. If I went bigger it would be a very small lift and the pinch weld mod. But because this is a daily driver and also a long distance cruiser I need the capability of running 80+ all day long and you start modifying and it has the potential of taking away that capability.