They share bore spacing, bellhousing pattern, and C or W heads can be installed on the opposite blocks, but it isnt a bolt it on and go sorta thing. Windsor valves are all inline, side to side, Cleveland valves are canted, the intakes point one way, the exhaust another. Clevelands have huge free flowing ports that need a little filled in, Windsors have restrictive exhaust ports and a lowered factory intake that hurt power but can be fixed easily. A Windsor is a tall deck 302 with larger mains and a slightly bigger crank, a Cleveland isnt like them except in the ways already mentioned.

Clevelands were a Race engine Ford built, spawned from the BOSS 302 and they can make bottom end just fine. They have the highest flowing ports of any small block and can make power wherever you want them too under 9000 rpm and 6500 with no oiling mods. They were only built from 70-74 so they are more scarce than the Windsor that was built into the 90s in trucks. Desireability is what drives the prices up along with the limited availability.

If you dont have a Cleveland right now, then buy a Windsor and go that route. its cheaper because many 5.0 parts will fit it, such as heads, and the aftermarket is larger because of the sheer number of Windsors built by Ford. They can still make plenty of power but to match a well thought out Cleveland will cost about the same. Finding parts for Clevelands isnt fun, but you can look in magazines or a Jegs/Summit catalog and find Windsor stuff spewing from every pore with availability second only to the stupid small block chevy.

If you have absolutely nothing, the windsor is the way to go. If you already have a Cleveland, you are ahead of the Windsor to start but you will be using mostly stock parts to go fast. That means finding replacements, which is tougher than calling a speed shop and havin them send you one. They are both good engines with drawbacks and advantages of their own.

Clevelands are small blocks. Windsors are small blocks. Modifieds are small blocks. But M's have a 429/460 sized bellhousing pattern, and they use a Cleveland style head. They are a tall deck version of the Cleveland and a good source for 4" stroke cranks to srtoke a smaller engine (takes alot of rework to do that). Clevelands are a bit wider than Windsors and the exhaust ports are huge compared to Windsors, so fitting them in certain cars is a challenge. eg 65-66 Mustangs.