Good Morning!

Welcome to FABO!!

If you like slants, I say buy the shaumaker(sp???) coversion mounts for the slant to v8 conversion. That way, if you ever wanna go back to the slant, it wont take you long at all and you still have your original K-frame.
The 7 1/4 should live behind it well as long as you drive her gentle and don't get on it too hard. Id personally go with an 8.25" as it is a big piece of mind because that will indefinately handle it

Once again, welcome to FABO! and I hope someone fixes my spelling. lol