Mileage shouldn't really affect it
I agree as long as oil and up-keep was done right ,just that a shop like Roe's that sells their own line of cams and I'm sure have a back log of work may not be interested in just doing an install from someone who brings in his own parts ,and has over 120k on it,but you never know until you ask them :dontknow:
Plus I would never re-use a set of lifters that have over 100k on them and use those on a new camshaft .you could get by with the stock springs and pushrods but with that high mileage why wouldn't you replace them since you are there anyway ,,the Roller rocker you could get away with using the stockers but if you do go with the slow bleed lifters the roller rockers make it a ton better and easier to adjust lash on pushrod .the stock lifters have No adjustment in them unless you shim them or remove some material from the rocker stands .
I have installed 4 cams in both my trucks ,,the best bang for the buck and hp increase is to
1 choose your cam for what you want to do first ,don't just go for a good deal on one ,the best i got was with Crower stage 2 or 3 and Roe' s 710
2 slow bleed lifters
3 set of roller rockers - harland or crower sell them
5 good set of bee hive springs
6 .027 head gaskets on a stock set of heads will get you close 10 to 1 compression
7 good set of hardend pushrods
this will get you real close to 500 rwhp n/a
I got 501 with the crower stage 2 in my black truck ,when i went with the competition cams 270 hr on the first cam i did and this set up i was 478 to 485 on two different dynos