With the motor pulled out of the 83 D150 for a clutch and cam change this was an opportunity to flow that Slant head on the Super Flow 110.
About 8 years ago when I built the slant in the 83 D150 I put OS valves in the head and did some moderate porting, I did a lot of smoothing on the inside radius, but other than some minor blending no work at the valve guide boss.
I did have that head flowed by a company here in Indy, they used a Saenz 680 Digital flow bench and tested at 28 inches.
My Super Flow 110 tests at 10 inches, but there is a conversion formula that allows on to convert for direct comparisons, port flow tests ran at different inches of water.

the charts below show the results.
Remember, this is the same ports in the same head with the same valves tested on two different flow benches.
The two tests were ran nearly 8 years apart, but I cleaned up the ports and the valves so the second test was with parts that are representative of the parts originally tested.

My conclusions are:
The Super Flow 110 at 10 inches tracks close to the 28 inch test up to about 150 CFM, as shown on the intake chart. There is still some upward movement at the higher CFM levels at the 10 inches but it is at a lower rate of change. This indicates to me that the Super Flow test results in the .400 and above ranges are likely better than reported when tested at 10 inches.
The Exhaust chart shows good tracking across the range of readings as the exhaust flow gets close to the 150 CFM value but does not exceed it.

I found this interesting and confirms why larger ports with more flow need larger pressure drops to maintain test sensitivity.

I have other heads that I have ported since I did this head from the 83 D150. The later heads had a lot more massaging and showed a good rate of flow climb at the higher flow rates and valve openings. The comparison above makes me think they are better at the higher lifts than I thought they were.

I will have some time after I get the 83 D150 back on the road and I will do a similar comparison of the flow rates of the original ported 83 D150 head as tested above and some later heads and detail what was different among them.

The Y is CFM as mentioned.
The X is lift at the valve opening.

The flow bench has a calibration process using a set of plates with known opening sizes that allows one to establish exactly what the machine is pulling at that days air temperature and humidity conditions.
There is an accompanying coefficient table then used to correct the observed reading to a standardized test result.