It’s not hard at all to make 350hp with a 318 using 360 heads.
The real question is...... will what it took to make 350hp with the 318 be a combo that works well with the plans you have for the car?
It’s really going to be a different type of combo than say..... a 350hp combo built from a 360.
It won’t have the low end grunt you’d get from the 360 based combo, so you need more gear and stall to go along with the bigger cam you used to get some top end out of the 318..... which is how you got it to 350hp.
A true 9.5+CR, Mildly reworked 360 heads(215-220-ish @.500), fairly hot cam, nice intake/carb/headers.
Then pair it up with a 3500+ converter and 3.55-4.10 gears and you’re good to go.
The equally built 360 will be about 400tq/400hp.