An Unusual L-E

Hi, I'm new here.

Been around military hardware in a general way for my entire life.

I have a stock No.4 Mk1 and am familiar with the general Lee-Enfield and Lee-Metford platform, having shot and handled SMLEs and No.4's and 5's over the years.

This weekend I inherited from an in-law a sporterized No.4 Mk1. The reciever is marked No.4 Mk1, the fore-end wood and upper handguards are gone. The rear ladder is missing the aperature though the battlesight is there so it's "shootable".

The front sight is the standard No.4 type, but the barrel in front of it that usually protrudes is gone. Oddly, the magazine, unlike any other SMLE/No.4 magazine I've ever seen is NOT a solid bottom, but has a removable floorplate much like an M16 magazine. Lengthwise it appears to be a standard ten shot model, but it's not one of the Indian 7.62mm types either (seen those).

What can I do without dropping $30 on headspace gauges to ensure it's safe to fire? (Currently money is rather tight). Not in a hurry to fire it as I have quite a few other rifles, but out of curiousity.

Also, anywhere other than Numrich to obtain the sliding aperature part of the rear sight?

Headspace the quick way - click on the link.

Checking Winchester Model 94 Headspace the Quick Way