NO i really don't know much about switching from v8 to v6 except that its probably a lot of work i bet your truck looks good on 35's tho i hope to see a picture of it soon
If it was me, i would scrap the 4.3, and put in the lt1, im not sure , but you probably have 3.08 gears in the stock diff. front and rear. i would change to 3.73 gears if you plan on highway driving or practical use, but i woul go with the low gears if you just want a toy. i would go with the one piece drive shaft just for simplicity, but you will need to double check your pinion angle once you are done. it sounds like you are on track with a good project, keep me posted on how its goin.