The flexplate that you show in the photo is for use with the AOD or automatic overdrive transmission. The C4's flexplate is smaller in diameter. The flexplate that you need is an aftermarket piece only and was never used on a production Ford vehicle. You'll never find one in the scrap yard, so don't waste your time.
What you need for your C4 is a 10 1/2" (Torque Converter Bolt Pattern), 157 Tooth flexplate with a 50 ounce counterweight. Your torque converter bolt pattern will be correct for the new 50 Oz. flexplate.
There are several sources for them. Our forum has sponsors that can get one for you and probably with a member's discount. Summit Racing and Jegs are two mail order sources. Also any dealer of Ford Racing Performance parts as well as most vendors of Ford performance automatic transmissions will carry them, too.
Don't make the mistake of using a 10 1/2" 157 Tooth flexplate with a 28 ounce counterweight from the parts store. This will bolt right up, but because of having the wrong weight, will cause vibration and engine damage.
To mount the flexplate, I recommend using new mounting bolts, (Specifically for a flexplate. These bolts are shorter than those for a manual trans
. flywheel.), bolts of good quality such as bolts from ARP. Use a good thread sealant that has a high resistance to oil and temperature. Always use the circular backing plate that goes between the flexplate and the mounting bolts. This plate helps to spread out the bolt clamping force and prevents flexplate cracking due to vibration or harmonics. If you don't have one, get one. It's important. Ask for one when getting the flexplate or get one from the Ford dealer or NAPA. They don't cost much.
F.Y.I. about your engine. If it still has the original pistons. The 1986 5.0 HO pistons were forged from the factory, but there are no valve reliefs cut in them. This was on the 1986 engine only. If you are changing the cylinder heads, don't forget to check the valve to piston clearance. The 86 only cyl. heads had a unique combustion chamber design which, it's said, isn't very good for performance because of the excessive valve shrouding. It seems that Ford picked 1986 as a design/testing year. This head was dropped from use in 87 on Mustang's 5.0 HO, as Ford went back to a more traditional combustion chamber as could be found on the 85 and then 87 and up 5.0 HO.
I've personally done a 5.0 swap on a 67. Here's something else that may be of interest. The portions of the motor mounts that bolt each side of the engine to the chassis (Pedestals) may need to be swapped out with a set from a late year 66 or 68. The 1967 motor mounts and pedestals are a 67 only design. You may find that your new mounts are listed as being for a 67 plus several other years. That's wrong. The dimensions and angles of the mount make for about 1/4" of difference in the position of the hole for inserting the long through bolt into one or both sides of the engine. The solution is as said above. Change the pedestals and use the actual mount that is supposed to fit. Like that cheap set for a 68. To acquire an actual set of 67 mounts, as best I know, they'll have to be NOS and that means expensive.
If you fight the installation on your 67 and finally get the last through bolt installed by stretching the mount on one side as I did. You will experience a complete failure and separation of the rubber portion of the mount. The mount that failed for me was the driver's side. The engine lifted and the fan caused considerable damage.