I'm not really sure what to say, so the best would probably be to say nothing at all. But since that's not my nature, I'll wade in to a discussion with nothing to gain and everything to lose.
I know you've got to trust somebody, but it looks to me like you're trusting the wrong people.
If the previous owner claimed the build was from one of the "premier guys in the VW racing world", did he show you receipts? "Premier", according to whom? The mechanic telling you strokers are more prone to failure than stock-stroke engines-- has he built more than a couple of strokers? Because an increase in stroke can't make an engine less reliable in and of iteslf-- over-revving a stroker, yes; bad rod-ratio, yes; poor oil pressure, yes; cruddy parts, for sure; unknowing/uncaring assembler, absolutely.
But stroke as the sole determinate variable of reliability? I'm not sure what to say.
Lastly, buying an engine from a place that doesn't build them (Mid America Motorworks, JC Whittney, et al) means with near 100% certainty that you are buying a GEX, which is like flushing money down the toilet.
I'm not ripping on you. Over the years, I trusted a bunch of the wrong people too. I've had no less than 6 engines built, and it's only the last two that are really "right". Two of the worst engines I every paid to have screwed together were stock-stroke 1776s. It wasn't the stroke that made them reliable or not.
If you want to hold the stroke to 69 mm because you are looking for <100 hp, that's a good reason. If you want it because you've been told it's more reliable, that's not.
If I were looking for an honest 90 hp (not the "90" of the MAMW engine), I'd do a 1914 with Cima/Mahle cylinders, a counter-weighted crank, and H-rods (I could be sold on I-rods-- but really, the nice ones are $100 more). I'd get some CB Los Panchitos heads and an Engle 110 or 120 cam. I'd set the C/R at about 8.5:1 for the 110, or 9:1 for the 120.
I'd find a set of Dellorto 36s and get a CB hex-bar linkage, and port-match the manifolds. I'd come up with a Bosch SVDA distributor (w/ solid-state pick-up) somewhere, and run a Bosch blue coil. I'd cool it with stock VW tin (from Ultimate Powdercoating) with all the flaps and the thermostat, or maybe the Scat 36 hp tin with the flaps and thermostats added.
I'd get an A1 sidewinder in 1-1/2", and get a set of flanged heater boxes (also 1-1/2"). I'd eliminate the mechanical fuel pump and run the Carter rotary pump. I'd get a lightened flywheel, and a Kennedy stage 1 pressure plate. I'd get the entire rotating assembly balanced. This engine would run for 75-100K mi without anything but a bunch of valve-adjustments and oil changes.
It would also cost a lot of money. It'd be 3- 5x what a GEX motor would cost. It'd also be a real engine, and not "sweep the garage out" build. For another $1000 you could get an 82 mm crank, a bigger cam, and some bigger Dellortos and make 150- 175 hp, but we've already been there.
No matter what you do, please put disc brakes on the front before you do anything else.