After digging through a box of gifted LEGO for hours and only one piece of the instruction booklet left, I finally completed this. 6894 Blacktron Invader : r/lego
Lego Space Blacktron 6894 - Invader (1987) | eBay
Display Stand for Lego 6894 Invader or 40580 Blacktron Cruiser - Etsy UK