Here is an update and hopefully some math/concept checks from those on here that know more than me, which would be most of you.
I got the first of the two transformers done. The plans called for 20 wraps of 10 gauge wire I got 17 wraps of 12 gauge wire. Plugged it in and nothing blew up, so I checked the voltage out. I got about 15 volts out which is in line with 1 volt per wind theory on Microwave Transformer. I say about because I only have a cheap analog voltmeter.
Concept check: 12 gauge instead of 10 gauge should be fine except that 12 gauge will heat up faster thus reducing my duty cycle.
Math check: According to the label on the Microwave it was an 8.5 amp draw. So total watts is 120 x 8.5 =1020. So with my rewrapped secondary I get my amps out as 1020/15 = 68 amps
Now assuming that I can get the same output from my second transformer if I wire the primary coils in parallell and the secondaries in series than I add the volt and the amps remain the same. So my final output should be a welder that runs about 68 amps at 30 volts. According to the chart for 6013 electrodes for general welding, and recommended by atomic zombie welding tutorial a 6013 for light work should work just fine at 68 amps. and 30 volts may be on the light side but doable as well.
Any and all comments and additional insight is much appreciated. Another thought I had but I have doubts about is adding a dimmer switch to the primary coil inside to make it adjustable voltage. But I read that a light dimmer won't work with an inductance load. Is this because it will not maintain a steady voltage and may allow mild fluctuations, which is no problem for my frankenstien, or will just not work and if that is the case what would work to add voltage some sort of power adjustment?