I suggest Show-Cars.You can get a kit with everything that you'll need and they'll let you substitute parts like forged pistons for the cast pistons for the stock stroke engines.You can also substitute the stock replacement[door prop] cams for something more suitable for your project.I think that a kit that in the case of a stock stroke 348,would use the K-B Icon forgings for a 10-5-1 compression,and a part number 095o cam along with an Edelbrock Performer RPM single 4bbl. intake manifold .The carb ,in my opinion,should be the new Street Demon 625 cfm ,or the 650 AVS from Edelbrock.In your Beaumont[Chevelle] you're going to have to make,or have made,a set of headers anyway.