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30 years? You're the guy I want to speak to about this then. A number of my buddies are SpecOps type explosives experts and they are frankly doubtful as to the effectiveness of ANFO being the primary explosive in the OKC bombing. This is because (according to the SF guys) although ANFO can produce tremendous amounts of explosive pressure at the point of detonation, it drops off very rapidly as the pressure wave expands outward.

The Ryder truck at OKC was parked against a curb but about 20-25 yards from the wall of the building. My sources say that within 25 yards of detonation point, the blast would no longer be capable of cutting the hardened load bearing beams of a federal building which remember is usually designated as a "Disaster Shelter." They also point to some reports (tinfoil time) that residue of fulminate of mercury was scraped off buildings surrounding the blast site.

ANFO is pretty easy to create, but as you said it requires a substantial accelerant for reliable detonation. C4 would be perfect, but if you had either C4 or CEMTEX why fool with ANFO? But, I guess even a smaller ANFO device would do considerable damage if designed for a target other than toppling a building.

The explosive velocity of ANFO is about 13,000 LF./Second, the power comes from the tremendous volume of gas produced by ANFO. This volume is much greater than the powder needed to initiate it, say 40% gel which has a velocity of 16 to 18,000 LF./Second, but only produces 30% of the gas.
Remember, all that is necessary to cause the damage in Oklahoma City was to put the structure in motion, gravity does the rest, that is why the center collapsed.

I suggest you Google the Texas City disaster in the late 1940's, 2 ships carrying AN exploded at dock, the devastation was remnant of Hiroshima, it gave du Ponte the idea this might be a good commercial explosive.

The no. 2 fuel oil adds carbon to the chemical reaction, coal, oil sludge etc.. have been used for this purpose, but fuel oil is the easiest to handle and mix.