Not enough cons.

Delete the +1 health buff and make the ammo regen when not revved up. I like the ALT fire thing, but maybe lower the health you send out.

When active:
+infinite ammo
+10 hp on hit
+can give metal, health and ammo to nearby allies and engis
+while spinning up, heavy has 20% resistence to all sources of demage
+after taunt: heavy gets a 25% speed bonus
taunt: heavy breaks down his minigun and puts a dispencer
-after taunt, heavy needs to destory his disp to get the minigun back from the ressuply cabinet
-when spin up, heavy can not move
-15% demage
-15% firing speed
-20% spin up time
While unactive:
+15% demage vulnerability
All the time:
-30% healine from medics, dispencers and health packs
-all ammo collected becomes health

when active
+recharging ammo
+10 hp every second
+can supply ammo, metal to engis and health
-10 damage
-5 firing speed
-50 hp from medics

how about this:

+ 2 health per second
+ 2 ammo per second
+ act as a levle 1 dispenser for allies around you, but you do not produce metal

- when damage is taken, -1 health and ammo per second for 4 seconds (so when ever you are in a fight, and for 4 seconds after, you only regen health and ammo at a rate of 1 per second)
-

on taunt: deploy the provisioner as a building!
(if you taunt near the provisioner building you pick it back up)

the provisioner building basicly acts a level one sentry and dispenser put together, exept the sentry part has less range and more damage and the dispenser part has a bigger heal radius that gets better the closer you are the provisioner. and as long as the building is deployed you no longer have a minigun, and when you die so does your building. if you made it to the end of my comment, congratulations!

oh and you also get 50% less heal from dispensers, other than your building, 25% less from med packs and 10% less from medics

How do you Alt-fire with minigun when spinning up?
Also for me author's stats are already good and don't need forced complexity.
(Just a roaming Heavy's minigun)

this is what i think should be the stats

When equipped, you regenerate 2 health per sec
Regain 10 ammo per sec
15% more accuracy
Heals teamates except yourself when in alt fire
Alt fire will keep you stationary
-15% slower firing speed

although it might not come true, maybe the heavy can spawn near an engineer if that engineer uses the rescue ranger on him

I think the health regeneration part is a little far-fetched, as even with a 1+ health bonus can turn the tide of a Heavy-on-Heavy face-off. Of course, it all depends on when you spin down your minigun, but a health regen factor would change that drastically.

aoe healing when revved up(+3 per second and +5 when at full hp)
engineers can heal you by hitting you with a wrench (+20 hp, -20 metal)

alt fire PDA but instead
A: sandvich (-175 hp)
B: large ammo crate (-150 hp)
C: refill ammo (-1 through 100 depending on ammo needed)

can get sapped, aoe healing lost and -2 hp per second, can be destroyed with a melee hit or a heath pack

shoots syringes (at slightly higher velocity than medic's syringes, dealing 15 damage point blank, 8 mid ranged, and 2 long range)

+15% damage vulnerability

Pro:
+1 health + 1 amo per second

minigun rev creates a small circle of healing 5 points of damage (no meter to fill up)

Con:

1. 275 health.

2. Can not be over healed.

Yeah that seems pretty good, though the overheal should not be nerfed if you are going to lower his health.

(+) Regenerate health on kill based on target's max health (numbers below).
(-) -40% health and overheal from medics.
(-) -20% damage penalty.
Health:
125 or lower: 40 health.
126-150: 50 health.
151-220: 60 health.
Over 221: 75 health.
This is good for solo heavy play with a lot of health gained on kill but less everything from medics.

The Provisioner: When you swap out Sasha's ammo drum for a dispenser!
+ +40 Ammo every 5 seconds on wearer
+ +4 Health per second on wearer
+ Provides healing aura while spun up

~ Ammo supply is distributed to nearby teammates while spun up

- -50% ammo capacity (100 down from 200)
- 60% slower move speed while spun up
- -50% Maximum overheal

When yous spin up, you act like a dispenser for your teammates at the expense of (figuratively speaking) having the same mobility as a dispenser. Otherwise you can roam around the map independently more or less indefinitely.
A minigun aimed primarily at roamer heavies while also satisfying the heavies who prefer more of a support role. Combining the two is not recommended as trying to shoot at people while you have teammates nearby may suddenly result in a critical lack of bullets.

Dispenser that stoots
+ player and teammates gain 25 per second when spun up
- lose 2 ammo per second
- 50% healing from medics on wearer