As long as you keep it well lubricated, although not ideal, ali in ali will work just fine.
Your main problem will be the actual height and width of the engine.
The following figures will be rough guesstimates, but they won't be very far off.
Not only will your stroke be 5 times the piston diameter, so 75mm (3"), your crank throw will also have to be the same 75mm (3"), plus a bit of room in between to take into account of the crank webs, and if double acting, the stuffing gland and if not a wobbler type, a conrod as well.
So the crank webs would need to be about 85mm (3.5") diameter at least, then a bit of space, say 30mm (1.25") if a wobbler or about 175mm (7") for the conrod swing if using a piston or slide valve (at those lengths you would need some sort of crosshead).
So say you are building a wobbler, that would be around 90mm (3.5") for the cylinder, plus 30mm (1.25") for running clearance, then the crank webs at 85mm (3.5") plus say 10mm (0.4") clearance underneath the crank.
A total overall wobbler height of roughly 215mm (8.5") , or for a valved engine, 390mm (15.5").
For a wobbler, your cylinder swing would be rather large side to side, so you might find that the port holes will be excessively large to allow continuous running, if it will run at all.
In reality, if you wanted to try it, I personally would go for a maximum of 2.5 or 3 times bore diameter, even at the higher figure, things start to get a little out of hand.
I hope this has helped your decision.
John