Would it be worth it to get a memcal made up for my stock 304 for a power increase?
Yes. Easiest gain you are going to find after a good service.
Reaper
Cheers Reaper - I had a look in the owners manual and it recommends 20-40 oil.
Would a 15-40 be ok? or say a 10-40 magnatec?
you will find most people run 20w50 oil in the 304's