Aluminium for a 1978 Adams

[Astro2]

My apologies. I just posted this under mono hulls and realised this forum is the appropriate place. Sorry for double up.

I have a punctured a hole in my aluminium Adams 35 (circa 1978). After consulting several TIG welders and aluminium suppliers it was suggested I use 5083 but the welders are saying the difference in grade will lead to oxidation.
Question 1 does anyone have insight into determining the grade of aluminium used on the 1978 Adams out of Australia?
Question 2, The frame the hull sheets are welded to, is made of 10x40 flat bar. The suppliers of aluminium tell me they can only supply 6060T5 as no other grade is available. This is not the same as 5083. Is this an issue?