Xe268 cammed 360 and very light body

Yep just get that engine in and running as-is, it's already fairly 'optimized' as a combination there isn't really one part you can swap out for a big increase. Turbo ain't gonna be cheap unless you're great at fabrication and blower manifolds for SBMs are few and far between. Not to mention I have a Buick 3800 with the M90 blower and those are way too small for a 5.9L V-8; the biggest blower Eaton made was the M112 which is still borderline on a warmed-up 360, those are ideal for 4.5-5.5L engines. Funny video on YouTube of Richard Holdener testing either a 4.8L or 5.3L LS with a M90 supercharger and it killed a TON of HP. You can technically spin them faster with a smaller pulley but they become less efficient (makes more heat for the amount of boost provided).

I agree with putting a good converter in it and proper gearing, those will have the biggest effect by far on how the engine performs in the car. 350 HP in a 2,500-lb car is quite a bit anyway, do the math that's almost the same HP/weight ratio as a new Hellcat Challenger! A 360 will live forever at that power level too, you can beat on it all day and it'll just keep asking for more.