Original engine or Aluminum LS3?

[Braker68]

Hello fellow C10 enthusiast, I am new to this forum website but have been in the C10 scene for a while. I recently picked up an all original 1968 C10 long bed and it is my third C10. It has the original 307 (feel free to correct me if I am wrong on the V8 engine these trucks originally come from the factory) with the original 3-speed fully synchronized transmission. My question for you all is that if I should rebuild the original engine and transmission or put in a aluminum LS3 with (yet undecided) transmission? What would be the pros and cons for both set ups? And what transmission would you recommend for the LS3? In advance, thank you for viewing my post and responding. (Oh and one more thing, a build log will come in the future when I have more time in my schedule.)