Cylinder walls may be too thin.
Agree, since the VTX bore is 2mm greater.
78.74015748031496 thou = 2 mm.
From memory, a 0.060 overbore is as far as I've ever heard of working well....that would be 1.5239999999999998 mm, so I'm going out on the proverbial limb and saying, "No....I don't think it can be bored that far."
There are MANY here who are better bike mechanics than I, so don't assume that's the final word.
But, as a former engine builder who only built small block Chevys, let me also throw this out there:
Fair chance that even if the jug WOULD stand that massive overbore, what are the OTHER differences?
Besides bore dimension?
Would also need to know CRITICAL differences, like:
Wristpin size / length, wristpin placement in the piston, compression height, difference in stroke vs difference in connecting rod length, difference in shape / size of combustion chambers.
If stroke, or rod length is indeed different, does anyone make a stroker rod? Or a stroker piston, with the ring grooves still above CL of the wristpin?
Another Stroker Killer is case interference.
Where's it gonna hit?
And, alas and alack.....it's gonna be tough to predict....unless you are a mechanical engineed and can CAD it all out.
OR unless you spend the bux for custom parts, and mock it all up, only to find.....
As the man who taught me to build engines to turn upstairs and live, useta say: "Serious horsepower costs serious money; how fast do you wanna go?"
But I gotta believe: if the conversion you have in mind was doable, there would be ads showing stroker parts!