Since you're talking F16 loads, you might want to try a cheap and elegant 9:1 setup I devised. I have a detailed sketch somewhere. I will try to find it. It's pretty easy to describe, though, and works with narrow extrusions:

* A harken sheave for 3/8 line at the aft boom end, supported by a through bolt and spacers. (Build-your-own Karver.)
* A harken 2651 airblock floating block.
* A hole near the aft bottom of the boom, to act as a becket for the end of the primary sheet.
* A Ronstan 30151 cheek block at the front inside the mast.
* A pair of Ronstan 30151 cheek blocks mounted on the outside of the boom, to act as the upper blocks of the 4:1.
* A small hole mid-boom for the secondary line to pass from the inside of the boom to the outside. The hole should be placed in-line with the tensioned line to prevent wear.
* An eye secured to the end of the through bolt to act as a becket to terminate the 4:1.

If you place the blocks intelligently, this system reaves beautifully, and there is *zero* torque on the boom arounds its length, nor any significant block side loading when sheeted tight. The trick is to put the internal cheek block, pass-through, and eye/becket all on the same side of the boom.

You can *eliminate* out-of-line loads on the Ronstan blocks by using a pair of singles at the bottom, so they align themselves with the loads, and by sizing the blocks for the bottom of the 4:1 that have diameters matching the width of the blocks at the top, so the top blocks are not side-loaded. Finally, note that the cheek block on the hole/becket side of the boom must be mounted at 45 degrees (to suport the 90 degree line wrap) and should be mounted forward of the opposite block.

Finally, Do not use a long pigtail below the 4:1 to "save weight". If you sized the secondary line properly, you won't save weight by doing so, and lengthening the secondary 4:1 will minimize block side loads and extend the life of the system.

It's the simple, cheap, culmination of all my thoughts on what I wanted to do on my boat up until last week.