Your 248 will be a good strong street engine. Parts are getting a little harder to find but they are out there. Everything you need to know is in old posts on this site. The problem is they are almost impossible to find because the search feature here is a POS. Try doing your searches on Google, sometimes the posts here are easier to find with a google search. Once you find one start searching the posts of the guys who responded to that thread and keep looking. There is a lot here but it's all like a treasure hunt.
Here is a recent 248 build on the HAMB that went pretty far into GMC building.
GMC LINK This book by California Bill Fisher has a lot of good info mostly as an add on to the Chevy six info. The bad thing about building these engines is that California Bill's book is the last one done on them so there is nothing new since '54-'55. There are lots of newer parts that will work, like some small block Chevy valves.
Chevy, GMC, Buick Speeo Manual
