3 speed Manual to a 3 speed Auto in a 66

[T-N-T]

Howdy!
I recently purchased a 66 mustang with a 200 CID 6 and a 3 speed manual transmission. I will be doing a complete replacetoration (replacing anything that doesn’t look new) once I change the transmission to an automatic. My question(s) are: Is there a certain application of a 3 speed auto that will bolt rite in? I will also consider going to a different 6 cylinder to make this easier if I could order a long block and transmission that will bolt rite in. For example: Could I order a 6 cylinder long block and 3 speed auto for a 68 mustang and have it bolt rite into my 66? Or is there a kit out there for doing this? What type of headaches am I looking at concerning the drive-shaft length or spline lining up. Or what about linkage connections or the shifter lining up with the hole in the hump. Or the kick-down linkage, cooling lines, speedometer cable, etc. Do I need to have the console? Will the transmission come with the correct bell-housing? In other words, what is the best angle of attack on this. It is the first thing I have to do before I do the rest of the restoration. I am ready to order now. I have just over $6,000.00 in parts (interior, body, steering/suspension, brakes, etc.) ready to order now and another 5,000 allocated to this project. All parts are being ordered as if it has an automatic. Let me learn from your experience. Help!