You shouldn't need to upgrade the transmission, other than the clutch and pressure plate with more power. Toploaders are bullet proof, the T10's? I can't say, never had any experience with em, but I DO know they're somewhat less in terms of strength than a small block Toploader.
Suspension, brakes, transmission, rearend. You get the point......... it's no fun trying to handle all that power with 30 something year old suspension and brakes.
And don't forget about upgraded cooling. Your car probably came with a 20" radiator, even with AC. The 351W is a great choice. You can get alot of displacement in a stroked block. You might even check out the crate offerings, if you're not set on rolling your own. A good reason to stay away from the Cleveland is you just don't have the aftermarket support. What there is isn't price competitive compared to the Windsor. It also takes up more precious space under the hood.
An FE Stang with new suspension and stiffer springs will handle just as well as a Windsor car. There's not that much weight difference. Move the battery to the trunk and you've eliminated half the difference.
I think the tranny is a T-10, can't rember some one on the forum had me take a picture of the tranny and post it to find out what it was but thats been atleast 2 years ago and my brain has quit working.
Im leaning more twords the 351W now, I have front disk brakes on the car now with a new power booster and master cylinder, like I said earlier I plan on getting new disks up front and maybe putting a new set of drums on the back. The shocks in the front and back are only about 5 years old and they have only been driven on for about 2 years, the springs are all original so those need to go.
When we rebuilt the 302, that is in the car now, we put a large 4 core radiator in it so I dont think thats going to need any upgrading. I plan on pulling all the wires, hoses, and such and replacing every thing in the engine compartment. Number 1 just so I can run the wires lower down so they are hidden and so I can take care of any shorts that my have developed over the past couple of years. What am I looking at as far as clearance goes? My air cleaner already rubs the top of the hood on bumps. I have a hood scoop in the car (66 GT scoop) that I plan on making functional so that will give me another inch to inch and a half.
Thanks for all the help so far guys. This will be my first engine build all on my own so you guys taking the time to answer some of this keeps me from getting as nervous when I go to buy parts.