Need to know the diff/ from gen 5 to 6 454 and gen 5 and 6 502 and the diff/ between tall deck and short deck blocks. And is the merc. 525 a tall or short deck block ?? thanks

I'll take a stab at this:
The 454 is a 4.25 bore, the 502 is a 4.5 bore
The tall deck blocks allow for more stroke, = more torque
The 525 is a 502 reg deck block
Someone else may be able to explain Gen 5 and 6?
The casting numbers and the block can be looked up on line for ID.

http://www.offshoreonly.com/forums/d...-5-vs-6-a.html

Gen V blocks have a stamped steel timing chain cover with 10 bolts. From the factory have a flat tappet camshaft, peanut port heads. The mag engines have the rec port heads.
Gen VI blocks have a composit timing cover with 6 bolts. They have a roller cam, with vortec large oval heads on the 454. The Mag engines have the rec port heads.
All of the Merc engines are standard deck height.
Some of the old Merc Racing engines were tall decks. Like was said you can stroke it up to 4.375" with a tall deck. With a standard deck you can only go up to 4.25" stroke if you use offset pistons.

now can i use a 525 intake and heads on a tall deck block, and will a 502 crank and rods work in a 454 block ,i know the pistons will not because the bore is to big.

A standard deck intake will not work on a tall deck. The crank should work.

Not to be picky, but a tall deck (10.2") can accept up to a 4.750" stroke. I don't like going over 4.5" stroke since you end up with a very short rod and steep rod angle.
The Gen VI 502 has a stock bore of 4.468"
Eddie

The heads will work fine. As will the crank and rods. They are the same from the 454 to the 502. You are right that the pistons will not work. The only way to make the intake work is to use spacers. There are a few companies that make spacers to put a low deck intake on a tall deck. You will have to run 2 sets of intake gaskets, one on each side of the spacers.
Eddie

thanks evey one, any of you guys know where a 502 standerd bare block is laying around so one would what to get rid of i have every thing i need but the block??

If you use the 525EFI heads, then you will have to use 525EFI exhaust. They are a modified Edelbrock head with a different exhaust bolt mount pattern.