Overdrive options

Quicktime makes a bunch of transmission adapters, including ones for SB or BB Chrysler, that will fit a GM 4L60 or 4L80. The 4L60 is a smaller trans with a deeper 1st gear (like a smallblock A999) and the 4L80 is much bigger, stouter, and with ratios similar to a 727. There are non-electronic versions of both transmissions, but I don't know as much about them.
The 700R4/4L60 is not electronic except for the lockup, later 4L60E and 4L65E are all electronic. The 4L80 has always been electronic, pretty stout and based on the THM400.
In real world situations, I suspect that many would not ever miss the fuel economy benefit of the lock-up torque converter. Just my suspicion. So long as it was all "factory stall" levels. If you were using a 6-cyl LU converter behind a healthy V-8, then it would be a higher effective stall level than the V-8 converter would have been, so getting that smaller converter to lock-up for road speed could be of benefit, but not by very much.

The LU converters need their own input shaft, as I recall. PLUS, from experiences, a good heat treat on the converter splines for durability of those splines, on ANY reman LU converter. You never know when it's going to "spin-out" and the car stops moving. I know from experience with my '80 Newport360.

Best option is to get a normal converter and matching hardware.

The 700R4/4L60 is not electronic except for the lockup, later 4L60E and 4L65E are all electronic. The 4L80 has always been electronic, pretty stout and based on the THM400.

GM's lock-up converters have always been worked by analog electric vacuum switches (to lock and unlock depending upon part-throttle engine loads), plus the brake switch. All had an internal solenoid run by governor pressure, or similar, for the basic LU function.

The transmission with the electronic solenoids (replaces the various shuttle/shift valves in the valve body) will have an "E" on the end of their designation. The "E" transmissions should also have the shift solenoids and lock-up actions controlled by the ECM itself, or an external controller.

The only, earlier, GM 4spdOD "non-E" automatics which would maintain LU in OD, at WOT, were the diesel pickups, Corvettes, Z/28s, and police vehicles. Others would go back into "unlock 3rd gear" at WOT.

The earlier Chrysler LU converters were controlled by governor pressure vs spring pressure, and only in "high gear" or "OD". No HD applications or factory trailer package vehicles had LU converters. YET, the initial development of Chrysler LU converters were done on dragsters!

I'll just add that if the wild camshaft makes cruising at lower rpm tough, you might consider Rhoads variable lifters. Same PN for SB & BB, and I assume your RB. They work by leaking-down at lower rpm to give less valve lift, thus more efficiency and intake vacuum. At high rpm, they can't leak fast enough so lift is restored. Think of it as a poor-man's VVT (sporty Hondas and many others now). I have bought Mopar sets for $50 on ebay.
Whilst we're talking about LU Chrysler 727s:
The smallblock transmissions got LU, but bigblock models didn't.

It was attempted in the very beginning of a model year for bigblocks (so must've been in 1978?), and it was quickly abandoned due to durability issues. I don't know if it was a recall, or so few made that they just retrofitted non-LU transmissions if a car had an issue.

I have only 'seen' one such trans, a guy offered an NOS one for sale on Moparts when I inquired about possibility of a bigblock LU retrofit (perhaps 10 years ago?).

The shafting, VB, etc, from a SB 727-LU can be retrofitted, but reportedly the case differs from non-LU due to a fluid passage, and that's where the problem comes in. Perhaps someone could drill/tap/hardline a passage (I've seen such things done when I was a transmission test engineer) but you truly want to get it right the first time, not an area where you want to learn from mistakes. And at the end of the day, the 1-3% MPG increase isn't worth it.
I put a gear vendors od in my 78 Salon car with 3.23 sir-grip. Did it mostly on a lark and to split shift gears. Works good, I still have it today. No mods to the tunnel required, it bolted right on but did have to use the park dog from the old tranny extension and the drive shaft needed to be shortened. There’s a bunch of pics below for those interested. Total cost was about C$5,000 and that included drive shaft mods.