my understanding is you are correct on the mass of 318s but a police pursuit engine had different specs with upgraded internals. such as full groove main bearings/ HV oil pump, full time oiling to rockers with #2 & #4 cam bearing having a full groove, sodium filled exhaust vales, double roller t-chain plus the oil/trans/PS coolers and 3 core rad-HD 5/8" shaft 8 vain wp, 7 blade thermo-clutch fans

on the cam bearings I have not been able to source a new set as of yet and have only found them in a police code engine. the engine I got from Larry confirms this as it was a roller block with a flat tappet cam which is correct for the 89 4v 318 police code engine. IIRC the cam had .410 lift on intake but defiantly not a mass 318 flat tappet

I printed out some info on head casting #s and engine specs. it shows this 89 4v police engine as having 177 HP @ 4800 rpm where a normal 318 was 150Hp @ 4800 also showed that it was pre-magnum open chamber swirl port 360 heads with #308 castings and they ones I have on my engine. ( I forget the other head casting #s Imwill recheck them)

that may also be where the slightly smaller measurement of the 360 port size comes from with the later model 360 swirl port open chamber heads. as the 915 intake talked about earlier was on the 89 police engine I have. gave that intake to member (locomotion)

so the early non emission 360 heads 72-84? have the larger port opening and are not a swirl port chamber and the late model #308 heads where labeled as swirl port chambers along with the #302 head introduction in 85. 360 went roller cam in 89-91 so that may be when #308 head came out? but either way the #308 pre-mag head is the best one to find but prone to cracks.