Tom,
Yes I would agree with Bigkidz about isolating the LA150 with some sort of points...either a sistrum rack or walker valid points. I have tried both and they do make a nice improvement.
I would also highly recommend an upgraded power cord. I have use a number of them with varying results. I am partial to electraglide products but also had good luck with Silent Source which are moderately priced and marketed by Walker audio. Power cords and IC's are so system and ear dependent that the best advice I can offer is trust your ears to get the combination that sounds best to you.
As far as tube rolling is concerned, Jud Barber already uses NOS tubes in the unit so that is not an area that you can improve on really.
I love the LA150 and have it mated up with a Joule 80-80 which is a dynamite combo.
If you need any other help, email me off line and I will be glad to provide any help that I can.
Happy Thanksgiving!!