Not a bad plan at all Jim, you need to have at least one of these running at all times, and if the 73 needed rebuilt anyway, a borrowed part is not the end of the world even for the purists in our group.
You might want to take the opportunity to pressure wash that thing since you are pretty far torn down, now would be a great opportunity for that and will also give you a clean slate to watch for any fresh oil leaks in the system. Not to mention getting it dolled up for glamour shots. (centerfold anyone???)
As far as how much time in a weekend, usually it goes like this, the more "fun" you are having the faster the weekend disappears, but if you are working or otherwise dealing with an adversity, time will come to a standstill.
I have had some weekends fly by and some others take an eternity. Just don't have too much fun or it will be gone in the blink of an eye.