I was under the (apparently mistaken) impression that anything over 25 years old was not smogged in CA? I know NV is anything made in '68 or before is exempt in the two counties that require smog. But, if it were me, I'd get a 360, mill off the 360 on the left front of the block (as if the inspector would ever both checking), stamp 318 on it, bore and stroke it to 408ci with internal balance and nobody but you will know what's inside. I highly doubt they'd ever know the difference between the one motor mount and the rear main cap/oil pan difference. Add some smog legal headers, smog legal intake and carb, little more camshaft that'll still pass smog and you won't know it's the same truck. I'd honestly not even worry about the 360 stamp.

OR, you could just get a 360 from a truck of around the same year and transfer it over. Make sure to get the flywheel/torque converter, the harmonic balancer, the 360 oil pan and the motor mounts (one of them is different but I don't recall off the top of my head which one). If you have an automatic transmission, B&M makes a flexplate that you can use to bolt up to the current converter that will balance the engine at the back. 360's are externally balanced which means there's weight removed from the flywheel and added to or removed from the balancer and torque converter. The piston and rod assembly weighs X amount and the counterweight on the crankshaft has to counterbalance that. On a cast crankshaft the density of the iron is not what it is on a forged crankshaft so there isn't enough weight in the counterweights to offset the pistons and rods. So material is added to the ends of the crankshaft in relation to the counterweights on the front and back. Anyway, perhaps everyone already knew this, but if anyone didn't, they do now.