All the accessory brackets, pulleys, you will need to be careful with your intake manifold and air cleaner choice if you are planning on staying with the stock hood. You may have issues with brake booster clearance depending on what style of valve cover you choose. Another issue you may find is longevity of the T5 behind the big block. They will munch gears behind much lower powered motors, so you may need to be careful with the big block. They can be built up as the Fox body Mustang crowd has found, but you are looking at spending some $$$.

 

the rear u joints could all be changed to something heavy duty or find a stock 427 driveshaft and yolk

 

Was the car originally a big block? I have a 1968 L71 car and have owned it for close to 28 years. A Big Block Corvette is a lot of fun, just choose your parts wisely when building it. When I built my engine the aluminum big block heads were VERY expensive and all were "Open Chamber" style heads. Do you have heads for the car yet? When I rebuilt my 427 I wanted to make power and use lots of compression but most of all I wanted reliability. I used a "Closed Chamber" head and I can drive my 12.25-1 427 in the middle of August here in Virginia without any pinging on Sunoco 93 octane. GM made closed chamber heads all the way into the early 1970's before they were dropped in favor of the better emissions from the open chamber heads. The only down side is that open chamber heads ping, knock and detonate easily. Even though I calculated the compression ratio three times I was surprised when doing a compression test I get 241-246 psi cranking in all eight cylinders.
I am using Hedman headers and they work great with the 1968. My car already had the springs and rear parts for the engine so I did not have to modify or change anything. I am using an aluminum radiator from Be-Cool and dual SPAL fans on a shroud.
You can search around but I used a Serpentine belt Conversion from MARCHE Performance, expensive but my clear coating has been peeling for a decade now.

It will be fun building your engine, take pictures and and take your time! After several months my engine was ready, the first time it fires up will be a big moment, be sure to have somebody record it for you as you will be too busy to do it yourself! If you need any thoughts please feel free to PM me. Good Luck!

 

Several people are running T5 behind big blocks. GM hates replacing stuff under warranty. Their torque ratings are based on teenage kids hammering the **** out of it at every stop light. They hold up well with a grown-up driving it. But you won't have to worry about u-joint or rear upgrades. The trans will spit gear teeth all over before the drive shaft does this.