need timing set info

replacing the timing cover due to it corodid,gone. im replacing all i can while im in there timing set, water pump, fuel, etc etc. my ? is the timing gears i took off are s-420 for the cam and the crank is s-493. all the sets i find around here at the local parts store are the same for the crank but the crank is a s-421. they both look the same other than the new gear the s-421 is off about 1/2 a toth if i was to put it on. my guess is that the old gear the s-493 is retarted abit. is it worth my time to seekout the 493 or is there much of a differance. gas milage, low end tork, etc etc. this motor is in a large box truck and heavy. kinda shooting for the gas milage. thinking of taking parts back and getting a 3 key set to advance or retart the timing. this new gear i gotten looks as though it will turn the crank clockwise a 1/2 tooth.is this advancing the timing. and what are the efects on power and gas with advancing or retarding.

can anyone suggest jetting for the for 460 with a holley 600 vac scondaries. motor seam to be pretty stock.73 heads etc. will a cam change out help on gas also,thinking an r.v. cam and do i have to replace the cam bearing if i change out

I'd use the straight up gears. Ford used the retarded timing deal as a stop-gap thing to battle the federally mandated emissions standards. The straight up gears should result in improved efficiency...

As for jetting,,,, I've never tried to use that small of a carb on a 460....How do the plugs look now, and what is the engine in, and how is it driven???? Would seem a 600 may have a tendency to lean out a bit with any heavy running with a 460.....