You can't get access to the float arm without dropping the tank, which I already did - actually twice in the last 3 weeks since my wife's also needed a new sending unit. I can test the resistance next time I fill up, though the connector is a pain to pull off. I did test the new sending unit before installing and it matched what I read in another thread somewhere.
BTW, the biggest problem I had on both jobs was removing the breather hose "quick connect". I refuse to call it a "quick disconnect" as it took probably 30 minutes the first time and still 15-20 minutes the second time when I actually knew how it was supposed to work. I never found a good way to pop it off and ended up gently prying up the locking tabs with a small screwdriver - risking breaking it. On the second job I removed the breather hose where it hooks into the chassis as opposed to the top of the tank which is virtually inaccessible. It also needs a bit of lube on the O-ring when reinstalling.