4160 series Holley means only 1 metering plate with changeable jets. The rear is a plate ( which can be changed.......complete plate for plate )
Holley sells a kit to convert your 4160 to a 4150. The kit has another metering plate for the secondary (rear) side with changeable jets. I did this to mine.
I would just convert the 4160 to a 4150, drop 2 jet sizes and try it....
Holley also sells a jet assortment box...for about $40...with 30 sets or so
Lot less expensive than buying them at $5 a set