300-350 is pretty easy without stroking it, if that's not where you are going. I can say I love my 4" stroke 318... :)
To get 325HP, all you need is a stock set of 318 heads, a little bowl work, port match, stock valve size, or a bigger exhaust valve if you like.
Stock pistons, at zero deck.
Stock rods, crank, just have it balanced.
Stock pan, add a windage tray. (free HP)
Other adds would simply be a 500-600cfm carb of your choice, a small port single plane, or dual plane manifold, an offenhauser dual port is a beauty, and will make a 318 snappy. Some headers would help too. Or 360 manifolds.
Cam would be a 260ish adv duration, 450 lift, 106 or 104cl......
300HP, would simply be a stock 318, zero deck, with the cam, intake, carb, and headers, nothing special needed.
350HP, would require more extensive head work, etc.
Really, you should develop a plan on what kind of money you have, parts you have, or can afford, your capabilities, if you, or an engine builder is building it, if you are comfortable, or comfortable paying for porting, etc.
I know 25HP doesn't sound like much on the computer screen, but once you get over 1HP per cubic inch, HP gets harder to come by every little bit.
For example, a stock well tuned 220hp 318 from a truck I had, did the 1/4 in 20 seconds in a 5000 pound truck, 2bbl and all. 220HP, the time came out about right in the heavy truck from what I recall years and years ago.
I simply added an Edelbrock performer intake, and 600 edelbrock carb, took it back the next weekend, and it did the 1/4 in the mid 16's.... I remember the HP we figured math wise went up to 250HP. The motor also gained another 1500RPM of useable power. (with the tiny stock 248/248 cam)
My duster, had a stock head 318, with a offenhauser 360* manifold, stock compression, 600cfm carb, with the old 270/270 COMP (before I knew better) it ran mid 14's, I remember math said HP was somewhere around 300. (It WAS 15 years ago)
It took 3K worth of roller valvetrain, months of porting, and 8000RPM from that same 318 push that car 11.53. :)
So, think about where you are at with what you want, and we can help much better, instead of throwing builds, strokes, what ifs, and shoulda' coulda's at ya!