All the FE engines use the 6.488 rod except the 352/332 and possibly the smaller FT engines. Many rebuilders have now gotten into selling their own version of high performance engines since crate motors have been so popular. You may have what they refer to as a High Perf. 390, most of the ones I've seen usually have a better cam and head work as well as better
oil pump. You might check with the company, that's what it sounds like you may have.