Some questions.
 

Me and my friend just rebuilt his 5.0. He overheated it and warped the heads and the car was running like crap so we got an old 5.0 and found numerous differences.

When we rebuilt it we had to change alot of things.

The engine he got was locked up but for 100 bucks, had all new stuff the guy forgot an oil pump.

We took the heads off, and found different length push rods, different rockers, and found out that it was before roller rockers and roller cams were used.

So we put a flat tappet cam and changed the push rods and all that over and used the old engines stuff.

NOW We went to time it with the distributor and hes like last time we timed it we used the H.O. timing and it ran, and after we rebuilt it it wouldnt run on the HO timing, so we put it on regular timing and it fired right up.

MY QUESTION.

Can a cam change the firing order? I dont see how its possible unless when you line the two dots up it puts the pistons in a different order than the other cam does. Or is my buddy just not telling the truth when he said it was running on HO timing.

Also will it loose a ton of power by going from roller stuff to flat tappet?

the cam could in theory change the firing order... it decides which valves are open/closed and such. The cap and wires are the gatekeeper to firing order though. Those have to match the cam&crank's idea of what firing order should be.

Roller cam setup is less friction. Roller would normally be able to be a little more aggressive in the ramp rate and such.

No theory about it. Non HO cams use the 15426378 firing order while 302 HO cams(Mustangs, Thunderbirds, Lincoln Mk VIIs, '92 and newer trucks and 5.0 Explorers) use the 351 windsor's 13726548 order.
Roller rocker arms weren't used on anything except the '93-'95 Cobra.
Where you line up the cam and crank sprocket marks advances or retards when the cam opens the valves and has nothing to do with firing order. Most aftermarket timing sets have multiple positions to advance he cam for more bottom end or to retard it and make power later in the rpm range. Aftermarket cam grinds can have advance built in.
Yes it will make a difference but it will not be a huge loss by going with a flat tappet cam. You didn't mention what year the block was, but if it was cast during the roller years it will have two bosses in the valley. Drill these out and tap them for the bolts that hold the roller lifter spider in place and you've got a roller block. If not, you can spend over $300 and get a set of roller retrofit lifters.

Well what he did was kept his block because his heads warped and wouldnt hardly run at all.

We bought a locked up engine for 100 bucks and took everything out of it, and put into his block besides the crank rod and pistons.

It changed the timing, according to him. To 1 5 4.

He ran the numbers and he says it was a 68 torino engine..
It has blue valve covers.

Personally I think it came out of a truck.

It has a spot for a mechanical fuel pump in the timing chain cover as well. Which I think all do.

It has like 3 X's on the block and says 302 underneath the lower intake.

Had a 2 barrel intake on it when we got it.

*UPDATE*

Theres clearly a problem somewhere with the build cause the OIL looks like a milkshake.

Uses 3 gallons of water a minute.

Warped/Cracked head? Or is the older style heads not matching up with the newer style block?? What could be wrong?? New headgaskets and all that were used. Heads were torqued properly. We did a build from the pistons up and added a cam.

If he overheated the engine bad enough to warp the iron heads, it most likely cracked the block and/or at least warped it to hell too. What do the heads sit on? That would be the deck of the block. It will warp just like the face of the heads. Plus the late model blocks are a lot thinner down in the webs than the old ones so they're more prone to cracking when abused.

The older heads won't matter. I've had '66 289 heads on a roller block in my first Mustang. The head gaskets can be put on incorrectly but, they clearly have FRONT stamped in them so it would take a monkey to mess that up.

If the original block wasn't checked out and decked then you basically answered your own question when you said it was reused after being overheated and badly warping the heads. The heads have a much thicker surface than some areas of the block.