Hi JP,
Sperex is from the Holts range of products, its temperature range is up 650 deg/C. so should be OK, I've used Halfords' own brand for my F.
As to getting the old paint off, it's a question of finish. I completely stripped the engine, degreased the crankcases with \"Gunk\" and put them in the dishwasher, (remember to remove the gearbox bearing first
).
The barrels and head, again degreased, them treated to a blast with a Karcher presser washer. When done greased/oiled up any bits that I don't want to rust.
All the bits were the sprayed using a VHT paint.
If you want a really good finish you'll have to have them blasted, I got some quotes, and some were just wild. Many wanted the engine in one piece with all the holes and bearings covered.
Goo luck with the rebuild and welcome to the forum.
Ride Safe
John