As a bystander who's totally unschooled in the mysteries of the BBC it looks to me like Pat's warning you that changing to the rectangular port heads is going to require you to make some expensive changes to realize any gain, and perhaps to not see a significant performance hit at lower in the power band (losing the big torque at lower rpm's). Sounds like the advice is to keep the peanut port heads, and concentrate on making some other small changes to improve what you've got as opposed to changing heads to something that's not going to be very street friendly. Just my $0.02, from reading & digesting.

Let is know what you decide, and how it works for you!