Slick 60's

I bought a set of 351w block hugger headers for my grandsons truck as this was what Sanderson suggested will work. Only problem was the passenger side hits the starter . The header hits the starter, which is the 2 bolt style. I've looked at the starters on evilbay which have the built in solenoid , but wondering how I would hook this up since I have the fender mount solenoid. I think that by hooking the positive side to the starter activation direct and using my present solenoid for starting as original it should work. Any questions, suggestions or drawbacks?

I am installing a T5 behind the 351w, and have a 3.73 rear end in the truck. Tires will be larger than stock 15 inch, just tires not rims. The transmission has the green gear in it and ma wondering how this will work out with the stock speedometer. Will this work out close to reading what the speedo should with the right mating gear for the cable and if so which gear?

Merry Christmas and Happy New year,
Rich