I think this would benefit me. How much higher should the bridge strap button be moved? A small amount like 1/2 inch, or something along the lines of 2 inches?
Unless you've got a slab-body bass with no forearm cut, you probably can't bring the strap button far enough around the lower bout to get the degree of shift you need. Even then, the strap button needs to be close to vertical, or the strap will simply pull off. It's also important that the new strap placement doesn't interfere with your arm.
Given those factors, you're far more likely to get what you need by using a rear-mounted flush Dunlop Straplok.
Using my Dingwall for a reference as to where to relocate the strap button on some other bass, is going to be useless. The ABZ has a short, light headstock, the body is scooped out at the butt end of the body, the scale is normal on one side and 3" oversize on the other, and the bridge is slanted...
The best thing to do, is try some balance experiments on your own basses, to determine the best placement.
The simplest method I've come up with, is to extend the back end of a strap by tying a shoelace through the hole at the end, dropping it down behind the back of the instrument, and then bringing it forward and upward so you can loop the lace around a volume or tone control, a 1/4" plug inserted in the output jack, or even a piece of bridge hardware.
With the lace looped over a suitable hang point, the weight of the bass will hang off that point as if it were suspended by a strap button somewhere on the back of the body.
Here's a test-fit session on my Squier P5:
Obviously, you want to be cautious. This is not the time to start jumping around like a jack-in-the-box, and I wouldn't do this over a hard concrete floor...
If the bass is still neck-diving, move the lace forward to the next hang point. If the headstock is trying to rise, then move the lace back to a hang point closer to the bridge.
On a P-bass, you have 3 immediately obvious balance points- Volume, Tone, and a cord stuck in the output jack. If you have an active bass, that's a bonus because you could have as many as 5 or 6 test points to hang your bass.
Once you've adjusted the lace and strap to your liking and the instrument is hanging at a suitable angle, you can mark the back of the bass anywhere along a line that the strap passes over. This will become your drilling point. I would recommend placing the hole just a little to the bass side of the center line of the instrument.
Here's a picture of my Dingwall, showing the geometry of Sheldon's Straplok placement:
Another couple of cautions:
1. The bass needs to be suitably supported while you're drilling the hole, preferably using a drill press to get good vertical alignment. Use a drill stop, to make sure that you don't drill unnecessarily deep.
2. You don't want to drill down into anything expensive inside your bass. Especially on a twin-pickup instrument, you need to be careful to avoid the wiring harness, pickups, bridge hardware, etc...
If you're not good with power tools, be SURE to farm this job out to a pro.
