Prune it so that you preserve healthy canes/trunks to transplant rather than a messier clump of crossed/dead/healthy ones. This will improve its regrowth after transplanting.

Is it to late in the year to prune?

I would like to transplant two plants in the spring, in the April , May timeframe.

Thanks

You can cut it back in late winter, before the buds open in spring. Cut just above an outward facing bud pair. Are you familiar with Forsythia? I would treat it similarly in my garden.

Since you will be cutting it back, perhaps you can force the branches as one can with forsythia. I've never tried forcing Weigela, but it might work.

Is it safe to say in central Massachusetts it can be cut back in mid to late March?

That's fine. The point of cutting it late in winter is that the plant is deeper into its dormancy. You don't care about the bloom of the weigela, so you could even cut it back right before you moved it.

Thanks Everyone