Double turbo project

[Palm]

How critcial is it that the turbo's are exactly the same in a twin-turbo turbojetengine setup? I understand that if there is the slightest difference in dimensions etc. there will be some loss of effect, is it negible though? Is it possible to use two different brands of turbo's if they are similar in dimensions. Sorry if it's an obvious question that it doesn't work, would however be grateful to get an answer. The reason I'm asking is because it's extremely hard to find two equal ones, unless buying new.