Using the method that Tom Kirkman describes for load testing,Does anyone know How much approx. weight will be needed to bend the blank to 90 degrees?
This is assuming that someone has done this before.
My second question : What is the best way to attach the line to the tip top when hanging the weight? Any special knot used that won't damage the tip top or put undue stress on it ?
Thanks

Tie the weight to a hook of some sort and hang that from the tiptop ring. On a large braced top, you can hang from the pair of braces holding the ring.

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What I do is take some old fishing line (preferably heavy braid), and tie a knot to the tip top. Run a few feet of line from this, and then to the other end, tie a clip of some kind, something that will be strong enough to hold a fair amount of weight (I usually use big coastlock snaps). The line should be short enough so that the clip hangs a few feet off the ground.

Then, I start putting sinkers in the 3-6 oz. class onto the clip, one at a time, until I get the bend that I want. With this kind of heaver, you're going to need a lot of weight, probably something on the order of a pound and a half, or maybe even more, so make sure that the clip you use can handle this kind of weight.

A rod holder really helps with this, too. I have one that I clamp onto my work bench, that works great. If you have a boat, you could do this outside, with the rod in one of your gunwale rod holders, too.

A bucket, filled with water is another good method for loading the rod. Makes it easy to load the rod in increments by simply pouring in more water.

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OK ,Here 's what I did. I tied a nail knot at the base of the tip tube and blank with 100 lb seine twine (small dia. line). Nail knot won't slip under pressure. I then ran the line through the ring and made a 2 ft hang. Worked perfectly and didn't get in the way of the fishing line on the reel. In all it took close to 10 lbs of weight to get to 90 degrees. My homemade jig (PVC strapped to an old B&D Workmate with two legs folded under) started the rod off at 30 degrees so I had to flex it another 60.
Thanks for the info guys. It helped me to get creative.