I have a 318 with a roller cam from factury and i have a hydraulic cam to pot in it, can this work going from roller to hydraulic?

hydraulic roller to hydraulic flat tappet?

new cam and lifters...
longer pushrods that still oil thru them

you might have to address some issues at the front of the motor..

is it a magnum engine?
make sure you order the proper cam to fit inside the timing chain cover...

just need to get flat tappet length pushrods. but if you have a roller cam, why not just get yours reground and reuse the OEM roller lifters? you can get the cam reground for probably $150 or less. you may need slightly longer pushrods after a regrind, as they get more lobe lift/duration by reducing the base circle.

bullet cams or delta cams in tacoma, WA, or hughes engines all regrind roller cams...

Well here is what happoned i ordered a cam hydroulic and lifters ,timing chain.manifold and a set of magnum heads to convert my 318 to a magnum but when i tuke it apart it was a roller motor from factery so i kinda paniced and stopped to find out if i can still do the swap.

Get a different cam and reuse the factory roller lifters. This way you won't have to buy push rods, and will have a much better set-up with fast valve action.