Summoning old timers please!

Got an old engine to revive my S5 (no, really, the square stroke RB S5). It must be some early engine from RB because I can't seem to find any picture of mention of it. Here's some clues:
-Purple head (in the style of the first S7 but with less fins);
-C5 case like my S5;
-5 port liner with divided inlet port, square stroke like the Sx engines;
-the head has the glow plug button incorporated like the S5.

I'm at a loss here, a purple head RB????

I dropped a new conrod, S5 crank and head and I like how it goes with a 2058 pipe.

Huh?! A CS Sport? Has anyone heard of it?
Paco to the rescue!