That is a tough one.I think 315 is the heaviest screw in field point being sold now.You can go a little heavier by using 125 gr steel adapters,then a glue on head.You can put lead in the hollow cavity of the steel adapter and may get 20 grs there if it is solid lead.
I have made 318 gr heads but didn't need to go any heavier.I'm not sure if you can get as heavy as you want or not.I just haven't figured out how.I guess where there is a will,there is a way.It woul almost seem like it would require some custom parts.
I know you want point weight but instead of an aluminum external footing,how about brass or stee? I don't know how many grains that would be but it might help.
I hear some say that there is a difference in whether the weight is in the point or insert but in my shooting,I just can't see it.Not saying it isn't so.Good luck.I'd be interested in hearing what you come up with.