Sorry for the loss of your father-in-law. 

While I'm sure you will miss your Beaumont, the Mustang has a lot to offer - most importantly the times to be enjoyed with your son.

There will always be more old cars out there to get when the time is right.  In the meantime you have a great car, which is basically a new car, to enjoy.  Have fun with it!

FWIW, I was looking for an affordable old car for a long time.  Finally found one that was at a price I could afford but it did have some rust issues that would have had to be dealt with in the future.  Deal fell through when somebody offered the seller a few hundred more than the agreed-upon price and I found out it was gone just after I returned from the bank with my cashier's cheque in hand.  To make a long story short, in my searching after I got over the disappointment, I happened upon a 2006 Mustang GT with some 36,000 km on it, lots of options including interior upgrade package, black with red leather, no rust anywhere, and just a nice tight car for just a little more than the '69 Pontiac Custom S that I missed out on.  It 'only' has 300 hp, which is still a blast to drive, handles great, brakes great, has A/C and other creature comforts that all work like new, and I couldn't be happier with it.  Looking back now, one door closed but another opened, and I am much better off with the Mustang than the old car that was going to become a money pit.

I still want to get another old one some day, and I will, but for now I'm enjoying carefree summer cruising with the newer car.  Works good, sounds good, does all the right stuff without the headaches of the old one.  Each has their place and the new ones don't have the character of the old ones, but I guess all I'm saying is that I'm not suffering, if you know what I mean.

Enjoy!