"Panel mount" resistors

[maxhifi]

Looking to replace some flat wire wound resistors in the 50W range, I see there's tons of options for new style finned aluminum panel mount resistors. Is there anything I should be aware of before making such a substitution in vintage equipment? Do these require the chassis to act as a heat sink to achieve their full rating? I have never used this new style of reaistor before. Really I would prefer to stay with the original style but availability and cost may present some issues.