I am using a GP 8oz tank on 4*40 with 46FX and with full throttle it lasts about 9-10 minutes. I think it is preety enough, the 8 oz goes in and comes out through former F2 without any problem, if you get a 10 oz or 12 oz, you could still fit it in, there is enough space but you should do this before sheeting the front tirttle deck.

as they won't pass between fromers F2.

8 oz is preety good in my opinion.