Ok...I'd say it's a 3550. A TKO is a 26 spline input.
Now, your pressure plate is a "Long" style pressure plate. It's common to Fords.....similar to a Borg & Beck style for GM.
I wouldn't fool around with having the assembly rebuilt. It's a lot less hassle to just order a new kit. The new kit will come with the disc, the pressure plate, and a new throw out bearing.
If you want it to be a painless choice, I would just call David Kee at David Kee Toploaders. He could tell you exactly what you need and send you whatever parts. He sells McLeod stuff.
You're gonna need a clutch kit with a good clamping force to be able to hold the torque of that engine.
McLeod makes a good setup....so does Hays and Ram. I would stick with a major brand.
An 11" or 12" setup would be fine....I would go with a Long type setup again. You'll need a 10 spline clutch disc for a Tremec tranny. A 4 speed Toploader is also a 10 spline, but I don't think the diameters are the same....so make sure you tell whoever what tranny you're using.
Go to
www.davidkeetoploaders.com , grab the phone number, and give David a call. Within 10 minutes, you'll have everything you need on its way to your door.
You can either call him, or go to the different manufacturer webpages and search for what you want. It's a lot easier to just call him....he'll know exactly what you need.