On a longer raked slammed, bike everything starts hitting, unless you have high bars.
If the tree was above the tank, you might get clearance with side notches, but lower the tree and all off a sudden the whole front of the tank is in the way.. so are your bats, if they are low.
When a bike is longer, you need more/most of your steering lock to turn tight, ie parking lot.
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Frame, unless only modding small portion, you should use a jig, otherwise it can move all over the place and never be straight.. it takes a logical thought out process to do it right.
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Flux core wire.. as far as I know it is hollow wire with flux inside to aid welding.. probably on a coil, same as solid wire.. for mig..
I am not much of a welder, but I think that is right.