Wow, I did miss a thread.
Bryanwheat, gave a good reply, But Ill go into a bit more detail.
The 4g63 dose come factory with 3 angles.
3 angle valve jobs became factory sometime in the early 70's I would say, maybe a little earlier.
Before that 3 angle valve jobs were for "Race heads"
The common 3 angles fall in these ranges, 15*-30* top cut, 44-45* seat, and a 60*-80* throat
Most are 30*/45*/60*
It gives the air flow a better path to transition around the valve.
Now the width of the seat is a factor also, A narrow seat width will not transfer heat to the valve seat as well, but get the widthy too wide and too much heat is transfered alowing for deposits to build up on the valve head.
A 5 angle is a "mis-term" you still have the 3 angles on the seat, plus the face angle on the valve and a back cut to the valve.
Why to have your Valves back cut
Now a true 5 angle valve job will have 2angles above the seat, the seat and two angles below the seat
Like 15*->30*, 45* seat, 60*->80* and still have the 2 angles on the valve.
Playing around I have done 7 angles with 2 radius, basicly it started on the side of the combustion camber and went down to the valve guide.
Now there is sveral diffrent ways to cut seats, old school is with a stone grinder set up, like B&D, Souix and others, this way cuts one angle at a time, and the stones get grooved and have to be trued, and it it is up to the machinist to set seat width, which can and will vary from seat to seat, and also seat palcement on the valve face. This equipment is still in use today, and is commonly found in machine shops.
Next would be a Nuway system, it is a bit more modern than stones, and it is alum bodies with carbide multi cutter inserts. It still cuts one angle at a time, but gives a smoother seat than the stone. seat width and plaement is still set by the machinist.
This equipment is still in use, and IMHO better than the stone
Next would be the Mira cutter, I want to say this was the first 3 angle cutter out, all 3 angles are cut at once, the angles and the seat width are set in the cutter blade.
The blade fixtures can be found in both live pilot and dead pilot set ups, I perfer a dead pilot style.
Commonly found with Petterson TCM head shops ( Seat and guide machine)
Next is the "Serdi" insert, there is a wide selection to choose from, ranging from 1 angle to 5 angles.
Seat with is set in the blade profile. Custom ones can be made for special custom cuts.
This is the set up I use. Retrofit kits are made to tool older head shops to use these blade inserts.
I would say this set up is common with the better equiped machine shops.