Roller rockers

So I have this "parts/core" motor sitting here (200 crank and rods bare head and block)

I was thinking of having this head and blocked worked over for when I build a high boost 250 (pretty much just swap rotating assemblies between the two motors)

I know the BBC/Cleveland rockers will work but how does one do it? the 250 uses a 5/16" bolt and the roller rockers I have seen are 3/8" or 7/16"...is there enough meat in the pedestal to drill and tap larger? I have some small cracks between a couple seats so it might already be goign out to a welder for a little repair and didn't know if I should have the rocker arm pedestals beefed up too?

with a stud mount adjustable rocker I will need a guide plate and the pedestal cut down shorter? (I had to have the pedestals milled down on my SBF heads on my s10 because the hex on the stud would hit the rocker and keep it from sitting down all the way)

Do I just need to find a GOOD shop to do all of this or am I over thinking it?

You dont need to go the whole guide plate route, check the Australian Yellaterra site and you'll see plenty of other ways of doint it.
However, if you not going to rev the arse of the thing you probaly dont need them anyway.
Are you planning to go turbo, supercharging? if you are the power is dependant on the turbo or blower airflow and the mass of air you can shove through the engine, the swept volume is secondary, and only really effects the rpm.
Are you talking about an Austrail high block 200 or your low block engine, our high block has much longer rods and bigger heavier crank, which Id prefer to use, Id seriously consider what you plan to do before you buy anything.
My thoughts anyway.
Jeff
A7M

The easiest way used to be to buy a set of crane roller rocker conversion guideplates.

I take it those are for a 315C Jack? (spying the part number on the box in the photo)

They are, but I don't know if those are even available anymore. If you find a set, they simply bolt on and you can use 351C or 460 roller rockers.

checked the website for crane and they still list them. They don't list the lower half of the stud size though (I assume the cleveland stud is 5/16"?)

guess I will need to order up a set here and some rollers (prob just some cheapies for now until I build a real motor up)

or should I get 35655-16 for 3/8" pushrods? I have a bare core motor I was going to transfer my stock parts into to finish and if I am investing in pushrods should I do some beefier ones?

motor will be boosted with a turbo and will be turning reasonable speeds (6000 max?)

5/16" stud on bottom. The set I had used 5/16 pushrods. 3/8 would be needed if you have killer springs and uber high rpm, but if that's the case these adapters are not what you want anyway. Also, the pushrod holes will have to be clearanced for the bigger pushrods.

If the goal is high rate springs and high rpm, I would machine the pedestals flat, drill and tap for 3/8" studs (not enough meat in the pedestal to do 7/16"), then modify a set of Cleveland guideplates by cutting and welding them.