Perry to perry all good. Plastic Victrix to perry, the Victrix heads dont have collars/necks, so you will need to ensure you only cut the head off. also use a 3mm drill, and create a shallow recess in the neck for the head to sit in. Or cut the neck and add a greenstuff neck to join head and body.
The Victrix light heads were very small and didnt really work. The Hanover heads and others worked, but were a pain to glue, all went to the USA with the rest of the Victrix metals.
Arms etc all interchangeable, although the Victrix and perry brit cuffs are different the paint will merge them.
Hope it helps