There are some kits that are manufactured to fit already registered chassied vehicles and others are creating hybrids with the (almost) complete mechanicals from one vehicle with a different body fitted.
As the basic component identity of the vehicle does not change, per DVLA rules , they would not lose their ‘right to registration’ and therefore would not require SVA /BIVA.
VOSA Clarification on Body/Chassis points rules
Some of you will have taken the time to find the rules that govern how much you are allowed to modify your vehicle before its identity is called into question.
Whilst the 8 points system has been in place for at least 27 years (in its current form) DVLA have been sadly remiss in making the guidelines relating to car modifying known to those that it affects.