Help needed with Rover V8 valve guides!

[MacHarding]

What is the correct length of shortened valve guides??

I'm in the process of rebuilding a stage 3 3,9 crossbolted rover v8 (for my TVR Vixen V8)
I've got a problem with installing the valve guides!
The heads are stage 3 heads (14 bolt) bought several years ago from V8developments - without guides....
I've bought bulleted and shortened guides...actually two sets, from two different suppliers in the UK.
NOW....my problem is: What are the correct length of shortened guides??
Mine are 59 and 63 mm long - both sets!!
But..have they been shortened??
I've mesured the standard guides in a 14 bolt Vitesse head (also late type guides with seals)and they are ap. 60-63 mm long.
The camshaft going in the engine is a Crane 232 - with 0.490" lift.

So...I'm a bit unsure of the correct fitted height of these valve guides???

The normal fitted height is 15mm - above valve spring floor.
So - to make room for the higher lift of the cam, I would fitt the valve guides 12,5 mm over the spring floor....right?

But by fitting the guides at 12,5 mm ... will the guides then sit too low in the throats??

Technical advice will be grately appreciated! :-)

Regards - Michael - Denmark