Everybody's pretty much covered the bases. If you're shifting friction, the primary issues are whether your axle is:
1. Spaced wide enough to allow the 7spd freewheel to fit in the frame
2. Spaced wide enough for the chain to be able to shift on/off the smallest cog without contacting the inside of the dropout/seatstay
If the 6spd freewheel is an Ultra-6, the outer face of the outer cog will be flush with the outer face of the freewheel body. If the outer cog overhangs the outer face of the body, you have a standard-spaced 6spd.
Standard-5/Ultra-6 is supposed to fit/work with 120mm rear axle spacing. Std-6/U-7 are supposed to work with 126mm spacing. Especially with Std-6/U-7, if you're retrofitting, you sometimes need a couple mm more. Mostly depends on how "fat" the chainstay and seatstay ends are at the dropout. Most frames designed for more cogs will have those ends profiled/thinned for more clearance, but an earlier frame may not.
I checked an '84 catalog, and the '84 Team did come with an Ultra-6 freewheel. Don't know if that means the rear is spaced 120mm. I'd a thunk they'd have gone wider in the rear by then, and the higher-end Fujis were Ultra-7, so they were 126mm. They likely went U6 instead of U7 to help hit the lower price-point, but that doesn't tell me whether they spaced the rear at 120 or 126. We didn't sell a lot of Teams, and my memory's flown.
You _could_ cram a 126mm-spaced axle into a 120mm frame, but it's not recommended. Better to widen the stays, and align the rear end and dropouts.
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Fuggedaboutit!