I have been mixing fuel since the early 80's. Started out with Castrol M oil until it was discontinued. Similar viscosity to STP, poured like honey.
Switched to Ucon LB 625 when it was availble locally in 5 gallon pails. Ucon LB is the same base as Klotz Synthetics. Many other synthetic oils out there but most all are compatible with Methanol/Nitro. Didn't use Castor till we started bumping up nitro from 40% to 50 and 60.
The 625 refers to the viscosity of the oil, 625 centipoise. Klotz used to publish their viscosity number for Techniplate and it was around 900 so it's thicker than 625. The Klotz Helioil is down around 400cp and they recommend mixing at 22%, probably to give a bit better protection. Heli's are not piped and likely use low nitro so I would not recommend straight Helioil in a high nitro application. I did pick up some Helioil but I mixed it 50/50 with Techniplate and it seemed to work well.
I bought a drum of 625 from a local industrial supply house in early 2000 and found out they stocked LB1600 ifor the oil industry as it was used to suppress foaming in oil/gas separators. They brought in a barrel of 625 for me with their regular shipment. I added 20% Benol to give protection from lean runs. Took 5 years to use up the barrel. It was a real ***** in spring to pump it out, 20 min/gal.
On the technical side, straight synthetic flashes a vapour at 500'F so it leaves little residue. However, a hot/lean run the oil will be a gas, not liquid and protection will be severely compromised. Castor on the other hand, thickens when it gets hot so it complements the disappearing synthetic. Your engine will "gum" up on a lean run and slow down as the Castor plates out on the sleeve/piston. Thus it prevents metal to metal contact. If you don't use castor, great, but don't let it run lean and especially if you use LB625.
Ucon LB oils are food grade so they are pure hence it can be used on food production lines with no danger of adverse contamination. Klotz or others may add something (red and racy scent) but none are willing to share their additives. A minor issue we had with pure Ucon is you couldn't see how much was left in the plastic tanks. These days, I use just SuperTechniplate at 20%. Easy to mix in 5 gallon batches (1, 2.5, 1.5 for 50). Tried 18% but took out too many pistons in 67/80 engines. Spares are expensive and hard to come by in the older engines so I am in it for the long run and the fun of racing. I leave to others to set records, deeper pockets I guess. Personally, I am slower than many but on average, I finish most heats. I'm the tortis.
For Buckshots sake, I will confirm that I use Rossi plugs from Mr Hobbs. Bought a couple dozen cards of McCoys MC 9's when the were clearing them out 10 years ago but I have prescious few left. I do have some issues with brittle breaking of the coils but I think I will try the suggestion of annealing them with a few cycles on and off to see if they last longer. Looking forward to testing the new Rossi X plugs should they be brought in in quantity. I think Al gets them 10000 at a time to get use the best prices. So they will be expensive for him to front the cost. Local shops are asking C$16 to 20 each so that is just not an option.
Sorry for the length of this but I thought some background to this discussion on plugs, er fuel, was needed.