will the magnum heads work on a stock 69 340 ,I think someone told me before there was a problem with using them I have a comp 274 extreme energy cam I want to get the heads from hughes. thanks

I thought the La 360 used the same head as the 340, there is a way to correct the problem? thanks

I called hughes and they told me the early 340's piston came out of the hole a bit, and to measure it to get an idea how much gasket to use. thanks

If your piston deck or dome is @ zero deck or less they will fit but you'd want to plug all the dimentions into here http://kb-silvolite.com/calc.php? to find your new CR and you would want your piston to head (quench) to be ideally .040". and to see if your CR is going to be too high. Cometic has custom head gaskets much thicker if you do have a positive deck plus thicker intake gaskets to restore your intake/head port alignment but there's been complaints about Cometic. Some aftermarket mag heads have LA intake pattern and some have the OE mag pattern which will dictate what pattern (need the same to match) on the intake you have in mind. head gaskets the same and possibly can elongate the bolt holes on the LA intake gaskets to work (not sure). Need mag valve covers though I think LA ones MAY be a close fit mag ones would be better. Need the mag specific head bolts/rocker arms/holdown stuff (MP stuff is OK here) and iirc can redrill for larger holddown bolts 5/16 to 3/8 for racing and or a high lift cam, might check on that deal. Plus pushrods and I would not order them until you mock up your setup & find your exact length needed. There are some Ford ones that are a bit taller or shorter (I forget which) than the std MP ones if needed. I would also drill/tap/set screw plug the (2) holes on each deck that feed the LA heads (reverseable if you go back to LA heads) and iirc you are just swapping heads but if you have the bare block on a stand in front of you, you could drill/tap the vertical oiling holes from the crank to the cam then plug them w setscrews & drill a 1/16" hole in each one as that is all the oiling a cam journal/bearing needs and alot of oil is lost past the cam journals. EDIT I reread your post and the 1.6 mag rocker ratio is going to change your (current 1.5 ratio) lift amt by a factor of 1.067, so yes VP clearance considerations also on the piston notches

hughes is correct in that the early 340 pistons stick out of the deck...

so if your engine has been rebuilt or is not stock..you need to check the pistons to see if they are above the deck at tdc..

if they are...you will need thicker head gaskets to maintain piston to head clearances...

so if your pistons are out .008 ...then get a head gasket around .055...you got .047 clearance..

The original cam will have to be changed along with the lifters unless you are one of the guys that will risk running new lifter on a 40 year old cam. You have to swap the lifter because the originals did not have an oil hole for the pushrods and magnums need pushrods that can oil the rockers, get new lifters and hollow 7.625 pushrods and you will be good there, unless you run a really thick gasket then you will need a little longer push rod. As for the oil hole in the deck of your 340 just don't worry about it, absolutly no harm will com from not plugging it.

As for head gasket thickness a stock high compression 340 piston typically sticks up about .018 or less bone stock and with the .051 thick felpro gasket will give you a .033 quench differance witch is perfect. compression should be just right for premium then.