Sbm x block

All X blocks came factory with 3.91 bore. All. Every one.
Its same as factory 318 bore
They are all over the place regards how far they can go bore wise.
Have seen and heard 4.125, and as small as 4.04 as well.
Zero need to install 4 bolt caps on it. I made a true 700 horse using one with the 2 bolt caps that block came with. 13.5 compression, 4 inch stroke.
They also were made with 4 bolt caps.