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.
Noticed your 89? 4 x 4. Wondered if you can give me a hand. Got a stock, 4.3L V6 98 Chevy Silverado Ext Cab, stock gears. Started this brand new after building BBC 69 Camaro, 10 sec car, BBC 70 Chevelle, 10 second car but now interested in lifted trucks. The thing is, I now got 35" 15's, 4" spindle, 2" rear block, 3" body lift and noticed big time gas guzlin. Is this 4.3L worth messin with or should I go SBC + gears and if so, what would you recommend. I acquired a LT1 complete motor from a 94 Buick Roadmaster along with the tranny and ECM. And as far as gears, I was thinkin about 4.11. Also, can I change the universal shaft to one piece vs. the 2 pc? Let me know what you think!