Funny you should mention Epoxy Mastic 121 Dave .... I have just used some of that to do my wishbones
Spraying would be quite quick but would tend to be a little wastefull, I would imagine it would need a fair bit of thinning.
Personaly, I would go for a small radiator roller ( Sponge one ) & flitch brush for the few areas that the roller won't reach
I brush painted the wishbones, it left a fair few brush marks .... Probably my own fault for using a soft brush that was a tad small
It gave the wishbones a cracking coat of paint though .... Just need to give them a light rub down and layer of top coat & the job will be a good un.
Nothing wrong with the finish as it is, just top coating out of personal preference
EDIT
5 litres should be stacks !!
The 121 I bought was probably 1 litre when mixed .... It took about 1/4 litre to paint all the wishbones & rear uprights .... I still have a fair bit left.