Other's I've talked too say any time you can unshroud any part of the valve is a gain. Sure not as much as an awesome short side radius, but with the port taper it's going to flow some on that side so still have a net gain. Loosing maybe 1.5cc's on that side isn't going to radically alter the compression.
I'm going to work on the exhaust manifold tonight, there is some bad casting flash in two of the ports and a few other spots that could use some opening and rounding. I've decided I'm going to drill it for EGT probes as well. They are 1/8" NPT threads, so I'll put iron pipe plugs in the holes until I pony up the dollars for the probes and IO box to connect them to the MegaSquirt.
Rebuilding an OHC Pontiac 250 with EFI and a Turbo