I had forgotten how hard it is to change spark plugs on a 351C in my 70. (It’s been 25 years since I had my last one). I changed the first one out on the drivers side and it took 15 mins. Are there any tricks to make it easier? The 2nd one of the drivers side looks even worse! There’s an engine hoist hook right there in the way!!! Any suggestions short of pulling the engine?
It’s a good time to upgrade to an electronic ignition. I use a couple extensions and a u-joint attachment. Depending on the plugs location as to what I used. On some it only takes the plug socket, on some add a 3 inch extension and others need the u-joint. It has been a long time since I did them with the engine in the car. But it seems to me it usually took me about an hour and a half to do them all.
Depending what brand you have on there pop the valve covers off, it helped on my 70. I agree there are an sob to change look on the bright side its easier than doing a 428cj.
Wow, I clearly never owned a 351C in a Cougar. In the '71 Cyclone, no A-C, I could pull all 8 and check them between rounds at the strip. There was one that I used the S-K spark plug socket that came with a hex on the end for - that way you can put a wrench on it 90 degrees - but mostly they were a snap. I burned myself plenty times.
When you thread them back in attach a length of vacuum hose to the tip. Much easier to get them started that way
I feel your pain, I haven’t found any tricks, #8 is the hardest for me, then #4 and then 7 so I start at the firewall first 
I got them changed but man was that a pain in the tail. I used a chunk of heater hose about 4 inches long to aid in starting the plugs back in. The 3rd one back on the driver’s side…I had to get to from under the car. The 3rd one back on the passenger side was a true pain also. I can’t hardly see where the 428 could be any worse. Mine has the engine hoist plates on each side between the 2nd and 3rd plugs. Is that factory???
I got it down pretty well on my first Cougar. Changed them many times in 150 k miles, never easy. Spark plug socket, 3/8" universal joint and 18" extension. The first thing I did on the current Cougar was to put in platinum plugs. I hope not to change them again. Don’s suggestion on the tubing for reinstalling sounds interesting. I typically use the socket to hold and guide some with the universal joint in place to add a bit of length. Pay attention to the angle of the plugs coming out, it’s a good head start going back. I had a Ford dealer mechanic tell me they undid the engine mounts and raised the engine for better access.
Did they look like this?
That is why they are often missing, folks remove them to make the job easier.
They look familiar but never used them. I guess it helps to have small hands and long thin fingers.
Don, yep that’s the engine hooks on both sides. Did it come front the factory with those or were they added later?
Those are the factory lift hooks.
I use a bent flex wrench with a 1" extension. You can slip the wrench in, get it to break loose, then unscrew by hand.
https://shop.advanceautoparts.com/p/sk-3-8-drive-bent-flex-head-ratchet-108-skt3770/22989167-P
Allenman85, why did you switch from a Cleveland to a Windsor and I’d love to hear how you got 622HP out of it?
Cost (at the time). The 622HP posts are already on here. Good heads, intake, cam, carb, exhaust make all the difference. It’s a full out race built engine so it’s not a lot of fun to drive for more than 30 minutes but dang it can still turn heads 