The stats I have in mind for the syringe gun replacement would be
x3 damage
-50% fire rate
-90% clip size
x2 reload time
selfheal increases as uber increases, up to 5 extra points per second
This would help an uber ready med survive a little easier, at the cost of most of their damage.

The stats for the others would make it harder to get an uber, and probably make up for lost damage.

I'd say the syringe replacement would fire a stream of lasers, or just one continuous laser, with unlimited ammo. The expense would be in damage overall. This makes the weapon similar to the other Doctor G items and make it a weapon that is easier to aim with given that the lasers wouldn't be affected by gravity.

I'd say that the medigun replacement would take longer to get an uber, but ALSO have a longer uber as a result. Or perhaps the uber comes with other benefits, like increased damage or increased firing speed, at the expense of invulnerability that is instead an increased heal rate.

Heres my take on the stats:

Primary: -Fire a projectile similar to the Mannmelter, but faster projectile speed compared to it.
- 250% slower fire rate (compared to syringe gun)
- 10 health on wearer (only 5 when used with Vita-Saw
+ 100% more damage (compared to syringe gun)
+ On hit: Anyone who damages the enemy hit by the laser recieves a speed boost for 2 seconds including the person who fired it (similar to solider's whip)
+10 faster move speed when active

Medi-gun: - Over-heal buildrate decreased by 33%
-10% slower healing speed
+Uber build rate increased by 25%
+10 fatser move speed when active

Uber provides the medic and heal target with a 30% speed increase (only 15% for scouts), 66% faster over-heal buildrate, 33% more over-heal, and 50% faster reload speed.

This combo was designed to provide a faster paced medic set that rewards team coordination, in exchange for a bit of medi-gun effectiveness.

syringe gun: fires a laser stream up to 5 sec before needing to recharge, unlimited ammo, 75% less damage

medi gun: 20% uber charge rate, uber last 4 more secs than default, uber decreases dmg by 70% gives mini crits and unlimited ammo and removes the need to reload (inceased fire rate on weapons that don't reload like the mini gun and melee) on target.

bonus:
when wearing full set 10% over heal and uber charge rate when healing other players with full Dr. Grordbort sets

Syringe gun: Projectile cannot be reflected
On hit: Enemy cannot be healed by medic for 4 seconds
+20% Faster projectile speed
No random crits
15% Damage penalty


Medigun: When you heal your patient, they become mini crit boosted
Uber charge is crits, and uber charge buils up 20% faster
15% slower healing rate