I personally think you made a great decision. The Td42ti are simplistic. Pushrod overhead valves with timing gears. Easy to adjust tappets. Easy to service. Can extract plenty of power and reliability.
Save up 450 bucks or so and throw her on the dyno.
an overly rich Td42 can run hotter due to too much fuel.
If you have an 3 inch turbo back exhaust
Top mount intercooler (which you do from factory)
The tuner can get the mixture perfect on 16psi with the stock HT18 turbo.
I think stoichmetric will be around 20 to 18:1 on full boost.
Thats basically good on fuel and not hot.
The cruise mixtures will be far leaner so even better.
In saying that though. I swear by this from what I seen.
A stock Td42ti factory cooling system that is in new condition can tow up a hill on a 40 degree day and it will not overheat or even move to the 2/3rd mark of the factory gauge.
If you require extra cooling because you are doing some extra heavy duty stuff then the following can help:
1) Make sure all parts are new (Thermostat,Viscous Fan, Radiator, Pump and coolant)
2)G35 Nissan Skyline Fan on original Viscous Hub (Thicker, Stronger and flows way more air through bench testing)
or
3)UFI United Fuel Injection Fan upgrade?
4)More toyota silicone oil into the fan clutch to make it lock up more
5)Thermostat With bypass difference (part numbers) TT2028-180 or DT79A(almost totally blocks bypass of coolant) The factory thermostat has to open 9mm to block the bypass at 100deg.
TT2028-180 opens 5mm at 85deg. DT79A From Mazda Tribute Basically early model. TT2028-180 from Peaguot or Hyundai.
Basically those thermostats are straight replacements. They virtually dont let any coolant bypass the radiator back into the engine. Just google it. There is more information
Everyone is slightly different but I use 60 water / 40 coolant.