My 914 didn't come with swaybars, so when I did the 5-lug swap I used the whole 89 911 Carrera front suspension with the stock 19mm torsen bars and underbody 22mm swaybay. The rear right now is just 180lb springs.

My car is V6 swapped, which means I have a whopping 20lbs of radiator up front and the all aluminum motor weighs 300lbs.
Tires are stock Boxster 16s. 205 ft, 225 rr.
The car understeers pretty bad. I like to drive it near the limits....

Would a stock rear swaybar @ 16mm fix it?

Another idea I'm considering is same size tires front & rear, probably 215 on 7x17 Euromeister Fuchs, since I could use new tires.

Thanks.

Remove the underbody POS and install a real adjustable bar.

Other ways of fixing this
Tires in square configuration
Add a rear swayer
Add more Rear spring
Reduce front torsion bar size reducing the spring rate
Reduce front swayer size - like I suggested up top.
Change shock pressures
Change tire pressures
Suspension alignment can also give you fits.

You could always go larger in the fromt and smaller in the back, Tires that is. Make it look like some of them Drag Hondas.

You can also just pull the e-brake, Oh wait its a 914

you can add a cutter brake

you can also do the same with the throttle if you have enough Torque to break things loose, or just lift that will change the orientation of your car.

Don't do the last one, unless you know what it is going to do, and need it for the situation. One of our Auto-xs they put a box on a banked section of the oval. The last run of the day I figured out if I just went into the box at full speed, I could lift and then immediately smash the throttle back down I would get through the box clean. It was designed to slow you down going into the finish. I crossed the line doing over 80 MPH. Corvette guess where pissed. 914 was just narrow enough that it would clear with just a slight rotation of the back end. Wish I figured that out 2 runs earlier. You can use the same technique at Mid Ohio.

Underbody sway bar a POS ? Seemed to work for 15 years on 911's. Only disadvantage is lack of adjustability. Eibach makes an adjusitable under body 911 sway bar with Heim join adjustable drop links.
Try what you have and make adjustments accordingly.
And where does one get 911 front torsion bars smaller than 19mm which are stock?
That would be a stock 914 front end or 911 SWB bars which are NLA.
Try what you have and change one component at a time or you will never know the effect of the change.

more rear spring

Open to that, but how much more? Besides the RH 200lbs springs what's available in stock size, or is it time to do adjustable coilovers and common 2.5" springs?

Rear sway bar is more spring, less front spring also helps. I put -4 torsion bars in the front of Carerror. She has 911 front suspension. Had to change the Elephantah bushings and A arms but everything fit. The torsion bar in the rear really helped plant the front of the car and I was hoping that I could use the stock front sway bars cause they come in 3 sizes.

The factory rear bar is something around 23 is pounds of spring.

If you move to a coilover you can get springs fairly inexpensively in just about any increment you like - the initial cost is a bit more though.