Jonathon, if it's "dry" I'd put 4 ltrs in it[but have more on hand] fire it up & keep checking dip stick after it's warmed up in Park!! Then just keep "topping" it up till you hit the full mark,little by little!! Don't over fill it. Doesn't hurt to drop it in gear once in awhile as long as you have brakes????
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Some times I wake up GRUMPY, but today I let her sleep in !!!!!!!!BLACKSTOCK Ont.
I use a very particular tranny guy and he likes to have the rear end jacked up(very safely) and run the trans in reverse gear and add as Pete says as the fluid drops. A buddy with a funnel to help is a good idea especially when starting for the first time , nice to have someone work the throttle also and monitor coolant etc. This sounds pretty exciting for you keep pluggin away.