Lids are useful. I went with aluminum because it's lighter and rust free, but it also cost a bit more money. On the lunette. Don't cut it and try to weld in an extension. I recall a few trying and it never works out, as in trail failure, which makes for a big bummer of a day. I'm trying to recall as I type but I believe the A-frame is just bolted/clamped to the tub frame, and it just C-channel. I would get some channel a bit heavier in gauge, to make up for the leverage from the extra length, bolt that on and get my length that way.
Or you could get fancy and build/modify your A-frame to accept some adjustable box tubing. Adjust long for the trail, shorten it up for the street. Many Farm supply places will have bolt on lunettes for such an application.
When you end up selling your trailer you can toss in the un modified parts, or sell them to the folks that like restoring to original. Lunettes are especially sought after.
Really plan out a SOA. Not the actual doing of it, that's easy, but the what you're going to end up with end of it. My CJ has 2 1/2" springs with a SOA lift and rolls on 37" tires. My M416 is completely stock and sits perfectly level behind my jeep with the lunette lining up evenly with my hitch bumper, no up/down adjustment required on the Pintle hitch.
I've banged that thing around a lot of places over the years and have neve once suffered a flat, on original tires bolted on in 1966. I think one of the few things where Uncle Sam might have actually got his monies worth.