Newbie (HELP!!)

Hello everone. I am new to the scene and need some help. I'm thinking of upgrading my 260 to a 403. Can n e one give me some help in what to look for, and where I can find a good engine for cheap.

Thanks

The 403 would be a drop in,with no mods. If I remember right,the 260 came with the TH350 trans,so no problems there.
403s were built from '77 to '79. I usually buy a rusty,running, 403 donor car.
They were availible in Buick B and C cars,and Pontiac Trans Am also.