Are you trying to do this on pump gas and alky, or race fuel and alky?
Here is what I would build:
.020 over 109 with a Girdle or 3 steel main caps.
Forged Crank and Forged Rods with Diamond Pistons
Compression 9.0:1 minumum 9.3:1 max.
Heads would be Aluminum and race ported Champion Or TA
Copper SCE, Cometic, or RJC head gaskets.
Cam would be a 212/212 or 218/218 hyd roller kit from a vendor
Ported stock intake with RJC powerplate.
Stock ported throttle body and doghouse
JW flexplate/ SFI balancer
Head Studs would be a real good idea
Balanced and Assembled by a Turbo Buick professional
Turbo 70GTQ or HPQ or the 67GTQ/HPQ
Stainless headers too. Stockers crack too much
RJC large wastgate puck or Precision 46mm/38mm gate
Transmission-(flames will be sent my way for this but whatever!)
A TH400 or TH350 with a manual valvebody and transbrake.
Heavy duty sprag and a front pump modded by DonWG(400)
I dont know the stuff needed to build the killer 350s
Nice big external cooler too.
Converter choice is tough,
I think my next one will be Bradco or Ultimate Converter Concepts
Other stuff you will want to add...
Chrome Moly Driveshaft and Strange or Moser axles
Rebuilt posi or upgraded unit for the 8.5
Upgraded Studs and Fresh Brakes
Rear anti-roll bar.
28"slicks or Drag Radials
Intank Double Pumper and -8 feed stock feed is the new return(flip filter)
AEM wideband, 35-60 psi boost gauge, tach and shift light.
No XFI, BS3, DFI, or FAST unless you have a tuner that teaches you how to use it and is always available.
Most think they "need" the big ECU to go fast, you dont, but in the right hands it makes it easier.
If not stick to the stock ecm, Powerlogger and chips. I like Turbo Tweak stuff.
Build A 9.50 combo if you want to go 10.0-9.90s
Now add cage and stuff if you want but you didnt ask for that here lol!
Hope ths helps!!