I am really glad to hear someone interested in getting a dial indicator...
In the past when I suggested this ( as the FSM shows to do ) all sorts of people told me I was off base....

I have had the Enco dial indicator for years.. but I got it locally... I got the straight arms/magnetic base with it at the time... maybe $30 for the whole shebang...

The locking fully articulated arms are THE CAT'S MEOW for nice... but are more expensive..

But I was in Harbor Freight a year ago...and they had a manager's special on a dial indicator with even bigger face than mine... both are the specs which RT mentioned. I got a beautiful China made dial indicator for $6..... Even if it was not accurate I don't know how they can make it and ship it to here and sell it for that...

So naturally when I got home I got out my feeler guages, my old Enco and this new cheap job to compare.... I could not find any difference in accuracy...

For full disclosure's sake... it is also possible to make that measurement by using feeler guages stacked ... etc.... and some way to mark the starting position of the valve... but that would deny you a good reason to add a most useful tool to your collection.... you WILL find other uses for it once you own it... but if this is the ONLY time you need it.. then borrowing it would be great for the first time...

If one does NOT have the fully articulated locking arm... then if possible it would be nice to make a ' bridge' over the cam area... preferably out of magnetic material such as steel... but could be wood or aluminum and secured in place...to allow the positioning of the dial indicator in line with the valve more conviently.. because the magnetic base does not sit very well on the narrow lip where the valve cover contacts the block...