It is a good bit of work to use the Jennings system because you have to map the ports, measure them accurately, and calculate their size. You then have some math to do to figure out the time/areas.

I have had good luck using about 130 to 140 for intake timing, and 150 or so for exhaust timing and leaving the transfer ports alone with the engines we commonly convert for airplanes. This all being for an engine desired to run below 8000 rpms. If you want to run higher rpms, and/or a tuned pipe, you will need to go with higher timing numbers, especially on the exhaust and/or with a tuned pipe. When going much higher on the exhaust timing, you will need to work on the transfer ports as well. It is rather difficult to modify the transfer ports, as they are hard to get to and you want to be very sure to keep their timings equal and at the same angle of exit as original.

AV8TOR