I just installed a set of Hooker competition on my 87 with a 350. They were suppose to be a direct fit. I have my front clip completely off and just the long block installed and i had a hard time getting them in. Had to notch the frame on the passenger side 1/4 " and redo the shift linkage to get them to fit. They had to be installed from the bottom with the starter off and the dipstick tube out. Still hard. You should use allen head cap screws due to not being able to get a wrench in to tighten them up.
I run Hedman #68310 on my SBC, The only problem Ive had is when the starter need repair/replacing the header need to be unbolted form the exhaust and the motor. some like Scofields but im not sure how they fit. I think on the El Camino ill try shorty headers from Hedman or hooker.