Hello and welcome to the forum...
To answer your questionz
Will the 292 head bolt on the 250?
Yes. It's a direct bolt on.
If so, does it have bigger ports and valves?
I don't think so. I know the valves are the same. The heads are essentially the same design. I believe the only real difference is the 292 head has the temp sensor built into the head, whereas the temp sensor is in the thermostat housing on the 250. At least that's been the difference I've noticed in the 250 and 292 I've owned.
If you want a real performance advantage I've been told that you actually want to use a head from a 194 cubic inch inline 6. Gives you a higher compressor ratio than the others. You can also shave/mill the 292 head but you want to check valve clearance to make sure nothing crashes in the combustion chamber. If you're running a 292 with the stock type (deep dish) pistons, you can mill the head quite a bit and have no piston/valve collision problems, and increase your compression ratio and the same time.
-ftyler
