I have worked with these ones too, I did about 30 min in 150 degrees C and then 10 min in the cooling oven with the oven door slightly open. I didn't have a lot of these beans and am not conviced that this was optimal but it is a point to begin with. I didn't achieve the chocolateyness I was hoping for but didn't have more to experiment with. As a reference I roasted pretty much the same as the the Papua (because of the large bean size of the Papua) and 5-7 minutes less than the Dominican which I found needed quite a dark roast. Perhaps I was a little light on the Ghana - I was erring on the side of caution and John mentions it does well with both a light roast and a dark roast, so perhaps you could go a little darker. Anyway you have done a fair bit of roasting now and tasting as you roast should hopefully get you where you want with these comments as a reference.
From what I've read (I'm in Guatemala so I have no reason to import cacao) the Ghana Forastero likes a high roast. Are you using an oven or a drum roaster? IIRC John had it at a final temp of about 290 for 20 mins or so.
Thanks for the suggestions. I'm using a standard kitchen oven, electric, not convection to roast. Haven't gone to a drum roaster as yet. That, plus a tempering machine are my next upgrades.
My usual roast on other beans has been 300 F (149 C) for about 20-25 min. so it sounds like I'm in line with your suggestions. Hope to start on this tomorrow. Weather here is expected rain (poss. snow) this weekend (southern Missouri). Therefore, no grape vine pruning in the vineyards for me this weekend. Will stay in the workshop with chocolate, someone's got to do it !