Are you sure about the engine displacement? I thought the tall deck truck blocks were offered starting in the 80's as 454's only, and the 427's were last made in 1970?? Is this some type of hybrid the previous owner put together himself? I'd break it down to find out what's inside before going any further.

If it is a production 80's truck engine plan on pitching the heads, the ports are smaller than the average small block. No point in adding the turbo with those heads as a restriction plate.

You don't want the pistons set down 0.400 in the hole, you want to maintain a normal squish band. Use the appropriate pistons. You could choose to take the advantage of the tall block and stuff in a 3/4" stroker kit.

You might want to rethink the turbo choice, even if it was free. This was a big, heavy duty turbocharger which would have a horrible spool up delay in your application. The compressor side seals aren't set up for a draw thru, marginal at best on a blow thru setup. Find a generic TO-4 on ebay for $200, you'll pay a lot more trying to making the 8-71 turbo work.

Good luck, Mark