Weil Mclain SGO with Carlin EZ gas T-Stat question.

There is no C-wire hookup on this combination.

We generally mount a transformer-relay unit such as an R8239A:

https://www.supplyhouse.com/Resideo-R8239A1052-40-VA-Fan-Center-w-SPDT-Switching-Action-Includes-R8222B?utm_source=google_ad&utm_medium=shopping_neutral&utm_campaign=Shopping_Neutral_LPLTV&gclid=EAIaIQobChMIrPvxps3Q-gIVQpFbCh1QMAcfEAQYASABEgJlivD_BwE

on a 1900 box in a convenient spot.

Wire your red thermostat wire from R or RH on the thermostat to R on the transformer, green to C on both, white from W on the thermostat to G on the transformer. Run the normally open relay wires outside the box through a Romex connector or bushing, then run a thermostat cable from these to TT on the primary.

This will constantly power the thermostat as long as the power is on to the boiler.