Help Identify My Engine

Good morning everyone. I'm new to the forum world and new to Mustangs. I recently purchased a 66 coupe for my wife's 40th birthday. The car was in pretty good shape overall. I had it painted, new interior, and tuned up, etc. I've been having a few issues with it running a little rough, hard starts, etc. I have replaced the plugs, wires, coil, rebuilt carb, new points, etc. The more I've researched and messed around with the car, the more I'm finding out it may be a Frankenstein car. Here's my biggest question. The block stamping is C5DE 6015F. To me this designates a 65 Falcon motor but is it a 170 or 200? It has 3 freeze plugs but the research I've dive says that early 200's had the 3 freeze plugs. So I found a tag on the coil bracket and after rubbing the paint off, it says 170 64 4F which indicates a 1964 170 ci motor. I know people swap things around in cars, and honestly I don't care which it is, but I'd like to rebuild it and the 3spd auto tranny. Any thoughts, suggestions, help? I just want to know which motor it actually is. Also, the carb does not look like any I've seen that should be on this car. It's a 1 barrel, supposed to be an scv but it only has an accelerator pump on the drivers side. No pump or other valve on passenger side. Please help!

That's what I'm thinking also but what confused me was the casting numbers on the block and then the tag on the coil bracket. Luckily I think most of the parts I have replaced thus far are the same for the 170 and the 200. Just have to double check the distributor and points gaps. Thanks for the reply.

Thanks for the reply. You're right, it has definitely given me a headache. I'm just picky and can't seem to get it running right and want to make sure what I'm buying parts for. From what I've read so far, these little 6's are hard to keep tuned up.