Alright, I'm feeling pretty bad about not keeping you guys up to speed with what I've been doing, so....
Let's tell you about one modification I did the other day. I found an alternative to the stock fuel level sender that fits our tank that requires pretty simple modifications. The stock style of sender is well hated in the Z world (same item, just different arm and float config) for being un-reliable and I though I'm not putting up with it any more.
The sender I'm using is from Classic Instruments. They have several styles but this one is the "Best". They come in various common ohm ranges, including one that is very close to our stock sender specs, ie 10-90 ohm. They have a 0-90 that should be pretty darn close.
http://shop.classicinstruments.com/sn36tThe 9" variety is EXACTLY the right length to fit in the 510 tank. It sits exactly the 1/4" off the bottom of the tank that is speced by the manufacturer. The 510 tank has plenty of areas where it could go, but just about dead center on top is fine, or just down and to the right of the vent nipple (on my 69 tank).
I drilled at 1.5" hole, then layed the sender in the hole and used the 5 holes in the rim of it to guide a 3/16 bit to make 5 tiny center punches. Remove the sender, drill out the holes to 3/16 then tap for 10-32 that matches the five brass screws they supply. apply the gasket, then thread the screws in, tighten JUST so. Not much meat in those threads with the thin tank material.
Add some terminals and wire pigtails, and viola. A sender that works, is linear and hopefully STAYS working for a few years.

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