one HUGE advantage of stroking the 318 vs. building a 360 is his '85 318 has a factory roller cam. that allows you to use either a reground factory or an aftermarket hydraulic roller cam with the very depandable and cheap OEM hydraulic roller lifters.

and a dippy is a heavy car. my 5th ave was 3950 lbs w/o me once I added the A500 tranny, big sway bars, 8 3/4" rear and 5 leaf rear springs (and deleting all the emissions crap, going to an aluminum intake). Torque is your friend, and torque is directly proportional to displacement. built identically except for displacement, I'd expect the 390 CID stroked 318 to make ~8%, or about 25-30 more lb-ft of torque than a 360.

the economics of it are use your existing 318 block, and spend $300 on a SCAT 4" crank, or spend $300 on a 360 core motor....otherwise the build costs will be very similar if you were planning on aftermarket pistons/rods/heads

for a car like this, that's going to be a street car primarily, don't look at peak HP, look at ave torque and torque peak, and let the HP fall where it may. a 420HP engine with say, 450 lb ft peak torque at 3500 RPM, with over 90% available from idle to 5000 RPM will probably feel stronger than a 475HP motor but with 450 lb-ft peak at 5000 RPM and only 70% of peak torque available off idle and 90% not available until 3000 RPM...