I have a pile of spare Tumbling Dice heads wearing the ubiquitous Scottish bonnet &, fortuitously, an equal number of TYW Revell musketeers. The heads are cast with a short nubbin where the neck would be.
The art of securely attaching one to the other is as follows:
Remove the head of the plastic figure cleanly at the shoulders using a sharp blade.
Using the largest bit in a pin vice, drill a shallow hole into the body of the figure where the head once was.
Apply a mixture of two part epoxy (for long term strength) & super glue (for immediate gluing ability) to the nubbin of the head.
Push the head, nubbin first, into the drilled depression.
Wait for the glue to go off (ideally 24 hours).
Undercoat. Paint figures.
The resulting figures look a little archaic for Covenanters of the ECW but are serviceable enough.