I'm upgrading to a hydraulic roller after wasting half a set of OEM flat lifters (and possibly ruining my engine).
I like the spec of the XR270HR. 1.6 Pro Magnum rockers and Comp Bee Hive springs are already in use so they'll remain.
Does anyone have specific experience with selecting pushrods for a retro fit? Comp offers a 7.29" and a 7.3" length. I'd like to know in advance rather than assemble and measure because of the time invloved with shipping etc.
The combination isn't too exotic so I imagine there's a standard somewhere.  

Call CompCam they should help you and also if possible borrow or buy a adjustable pushrod to get correct length.I bought the whole retro kit for mine worked out good.   WIEDER  

As Wieder stated pushrod length should always be checked. It's nearly impossible to guess the correct length with variables such as head gasket thickness, head milling, deck milling, lifter design, rocker arm design, etcetera, etcetera...  

I guess it's always better to measure first although I was hoping that since the modification is fairly typical, the info would be out there somewhere. Comp does offer a package and I'll take the advice and call them.
I was kind of hoping I could purchase all the components at once. I get duty/tax/brokerage free imports at the border if I plan it right. I live in Canda and order from Jegs or Summit.
Having to assemble the engine, measure and then order will slow things down, however that seems to be the wise choice.  

I just did the same, but I used the Edelbrock roller cam kit which came with cam,lifters and push rods. easy choice .  

That's my thinking too. However with all the variables, how can the Edelbrock people (or Comp) know exactly what length to supply? I would think that most combinations have common ground and so they would have a common pushrod length but that's the point of my question.
I'll probably skip the potential savings of mail order and purchase the pushrods locally after I've assembled the engine and measured.  

A couple of more questions on the upgrade.
As far as camshaft end play is concerned. What are the most practical and especially reliable ways of establishing and controling endplay in a retrofit?
Are thrust bearings behind the cam gear a necessity?
I like the idea of the Cloyes Quick Button timing cover and the Hex Adjust timing set with the thrust bearing. I just don't know if I really need it.
Any experiences?