I've read several places about the use of mustang suspension parts. But it was mostly forum talk. I run across that a couple days ago.
I'm still unsure about the 65 mustang spindles
Yes you can use almost all of the 1965 Mustang V8 Suspension parts many are the same as the 1965 Falcon / Comet suspension & steering parts. Yes the 1965 Mustang V8 Spindles will work and bolt right on. You can use your stock 1961 steering box if you want or you could use a 1965 Falcon / Comet steering box they are about 1 inch shorter in length dropping the steering wheel height so then you need to use a 1965 column or you would need to cut the 1961 column down a little to fit. There are also many later model steering boxes that can be used too.
So listed below is the basic parts list for getting the best in factory steering geometry using all the stock bolt on V8 suspension & steering parts. You can go with the 1965 Mustang V8 Spindles or you can use these same steering parts when using the 1965 Falcon / Comet V8 Spindles as well as the disk brake Spindles. Also all these Spindles and steering parts can be used on any of 1960 to 1965 Falcon's or Comets. I will be adding to this list as I can.
1. You can use your stock upper and lower A Arms if they are still in good condition or replace them with the new 1965 & 1966 Mustang parts.
2. Use the 1965 Mustang V8 Spindles with the drum brakes or without if you want to convert over to disk brakes. 1965 Falcon / Comet V8 spindles will also work the same as the Mustangs. These 1965 year spindles have the added benefit of the more correct steering arm height that greatly improves the steering geometry. See Note 1. below for additional Spindles that can be used in these early bodies.
3. Use the 1965 Falcon / Comet Non Power Steering Tie Rod Center Link only. The 1965 Mustang center link won't fit its to wide to work into the Falcon / Comet Chassis
4. Use the 1965 Mustang Inner Tie Rod Ends.
5. Use the 1965 Mustang Idler Arm and its mounting bracket. There is also a roller bearing idler arm available to make a Manual Steering Box Car much easier to turn.
6. You can use the stock 1 inch Pittman shaft six cylinder steering box (1960 to 1965) if you want there are other choices too.
7. If you use the 6 Steering Box or the 1965 Falcon V8 Steering Box (also a 1 inch Pittman Shaft get the 1965 V8 Pittman Arm.
8. You can use the stock 6 cylinder Outer Tie Rod Ends and Tie Rod Adjusting Tubes if you get a set of the Mustang Steve (MustangSteve.com) Spindle Bushings. Or you can also use the 1965 Falcon / Comet / Mustang Outer Tie Rod Ends and the 1965 Falcon / Comet Adjustable Tie Rod Tubes'
Note 1. Some people also use the Granada / Monarch disk brake spindles be advised that the steering arm is at a different height (see below for more details), these Spindles will use the stock 11 inch Granada disk brake parts.
Some additional Info on the Granada Disk Brake Spindle swaps they have been a popular swap and though they can also be used they are not the correct steering arm geometry for the 1960 to 1965 Falcons & Comets or the 1965 & 1966 Mustangs and will effect the bump steer going through the suspension travel during any spirited type driving, and after all that's one of the main reasons for even doing this swap. The steering arms would need to be precision bent so they match on both sides to bring them into the correct height spec. This ends up being about half way between the 1965 Falcon, Comet, & 1965-1966 Mustang Spindles steering arm height and the Granada's Spindles steering arm height so this require they be lowered about 3/4 inch downward. If this isn't something you can do properly or have it done then its going to be much better and safer to just use one of the Aftermarket designed disk brake spindles for the 1965 & 1966 Mustangs these will have the proper steering arm height to work right. Good luck on your swap.