I have the Comp XE 268 in my 68 road runner 383 engine. It has been in there for about 15 plus years, and 25K + miles.
The rest of the engine is completely original other than it has .030 dish pistons. I am sure the compression ratio is very low with the original 906 heads. I did not square deck the block.
I had a purple shaft in this combination and it was a total dog. No vacuum, poor in gear idle etc.
That cam was DC-280-110. Specs are 280* .474 106* with 60* overlap.
The road runner has a 727 with 3.23 gears.
I think this engine with the flat tops and other items the OP listed, along with the 4.10 gear would be a lot of fun!

Mark